Generally speaking, as a society we have come to understand that exercise is beneficial to the human body. Exercise helps decrease the risk of many chronic diseases, relieves stress, manages weight and improves sleep. We usually hear information in regards to physical fitness and benefits to the adult population, what about the children?
Strength training was once an unsettling topic when it revolved around children. More recent studies have shown that with proper supervision and appropriate exercise prescription – children can benefit from strength training, and in many ways will reap the benefits later as adults. A strength training program will increase a child’s strength, and although you may not be able to physically see an increase in muscle size, there will be an increase in the ability of that muscle group to learn how to control that movement. So, although children may not see the muscle gains that adults will with hypertrophy – they are still making gains.
“In preadolescents, proper resistance training can enhance strength without concomitant muscle hypertrophy. Such gains in strength can be attributed to neuromuscular “learning,” in which training increases the number of motor neurons that will fire with each muscle contraction.” 
Strength training has also been found to help improve bone mineral content in children. This study was questioning the ability of strength training to increase the bone mineral content in obese children, and mentions that obese children are also found to have thicker bones, but with overall less bone mineral content than non-obese children. There is a correlation between lean body mass and higher bone mineral content. The study proved this correlation true; the strength training program helped to increase lean body mass (meaning the children lost fat) and improved the children’s bone mineral content, even more so than the control group who only altered their diets:
"Previous studies on strength training in children have been scanty. It has been generally believed that strength training does not increase the muscle mass in prepubertal children and the strength gain after training has been attributed to neuromuscular adaptation….. We show a modest increase in total lean mass of 0.8 kg (2.4%) in the training group, which agrees with the previous 2 studies…..In our study, we showed a significant increase, 46.9 g (3.9%), in total bone mineral content in the training group at 6 weeks, which is in line with Morris’s study. There is also a trend of more increase in total and lumbar bone mineral content and total and regional bone mineral density at the end of the study in the continued-training subgroup."
As described so scientifically above, weight bearing exercise helps to strengthen the bone. Note that bones grow thicker with strength training. It is important that children are physically active and play. Running, jumping, climbing are all strength training type activities. These may not be your go to moves at the gym – but for children, the playground could be considered there fitness destination. Strength training can come in a variety of forms- not only bicep curls, push-ups and squats. Please do not bring your child to the gym and throw a barbell on his or her back. Running is a form of weight bearing exercise itself. Let the kids get out and play, and if you think they are ready, hire a professional to help them learn a sport or fitness skill.
“Mechanical loading is the most important determinant of bone strength, influencing muscle size and force, which in turn correlate with bone mineral density (Tagliaferri et al. 2015).”
Younger bodies are still developing and transforming – these bodies are learning how to move properly, and this is an important time to make sure your children have proper nutrition and are stay active. Bone adapts by modeling and remodeling processes, however the remodeling phase happens in the adult skeleton. Childhood is the opportunity to develop habits that will help grow healthy bones.
“(Bone) Modeling … occurs during childhood and adolescence. This process allows bone to grow in size and shift in space so the skeleton can adapt on the way to adulthood. Modeling is crucial to bone because it is in the modeling years that the peak bone mass develops – a significant indicator of fracture risk later in life (Rizzoli 2014).”
Some of the younger bone is still cartilage until it is finished forming. This is important in sports where certain body movements may affect bone that is not finished forming. In my experience, young softball and baseball pitchers, specifically, should avoid certain arm movements before the proper age (around 14 or 15). This is crucial! Make sure any coach or trainer working with your child is knowledgeable in his or her field. Your child is still growing and needs proper supervision when training to avoid injury.
Believe it or not - bone fractures have become a growing concern throughout the years for children. Bone fragility could be genetic or from lifestyle factors. In a clinical report published by the American Academy of Pediatrics, authors Laura K. Bachrach, and, Catherine M. Gordon, describes the potential risks of fractures:
"Vitamin D insufficiency and deficiency are widespread, calcium intake often falls below recommended levels, and physical inactivity is common among American youth, all of which may increase a child’s fracture risk."
Physical activity is important – and is far healthier than being sedentary. Consider that when your child is active, their bodies are learning to adapt, move and physiologically their bodies are also working to improve there overall function – bone is growing thicker and stronger, the motor neurons are increasing and the body is preparing itself to be able to move even better, tomorrow.
“Physical activity is known to influence both bone and muscle metabolism; therefore, inactivity – or decline in activity – can affect bone through those two pathways (Tagliaferri et al. 2015).”
Children that are not active will be more likely to miss out on the physiological benefits of physical activity – meaning, if they are not running, jumping, playing – they are sitting on the sidelines during the most important part of their bodies developmental phase (so to speak) – they could miss the opportunity to prevent future health concerns. If they are active, they will reap the benefits of physical fitness for years to come!
In a study regarding the effects of physical fitness on the child’s developing brain, researchers found that:
"Aerobic fitness was associated with increased gray matter volume in areas responsible for executive function, learning, and motor visual processes. Speed agility skill was linked to increased volume in two areas essential for language processing and reading. … 'Physical fitness in children is linked to a direct way to important brain structure differences, and such differences are reflected in the children's academic performance.'(F. Ortega)"
Did you read that? This kind of information bridges the gap between the nerds and the jocks. I was somewhat both, myself – maybe my childhood routine of after school sports inadvertently gave me an edge in the classroom? Thank you, mom and dad. I am taking notes…
Aerobic fitness will help your child in the process of decision making, learning and motor visuals – while agility and speed will benefit them in the areas of communication and reading. Strength training will benefit them in preventing unnecessary weight gain, increase their ability to learn how to control their body movement, and build healthy bones.
In conclusion: an all-around well balanced fitness routine (and proper nutrition), will help develop healthy and intelligent children.
Now that you have this information, I hope you can find ways to use this information to help make healthier decisions for your family. Recommend more physical activity, and less unnecessary sitting. Next time they ask why – you can explain the amazing super powers exercise will help them develop!
Sources & Cited References:
 “Strength Training by Children and Adolescents” - American Academy of Pediatrics’, Committee on Sports Medicine and Fitness; June 2001, Volume 107, Issue 6, pg. 1470 | Katherine Stabenow Dahab, Teri Metcalf McCambridge, MD, FAAP
 “Effects of Strength Training on Body Composition and Bone Mineral Content in Obese Children” - CLARE C.W. YU, 1 RITA Y.T. SUNG, 1 RAYMOND C.H. SO, 2 KAM-CHI LUI, 2 WINNIE LAU, 3 PEGGO K.W. LAM, 4 AND EDITH M.C. LAU3; Journal of Strength and Conditioning Research, 2005, 19(3), 667–672 q 2005 National Strength & Conditioning Association
 Idea Fitness Journal, June 2018, p. 34, “Bone Health, a Primer” by Maria Luque, PhD
 “Bone Densitometry in Children and Adolescents” American Academy of Pediatrics; Laura K. Bachrach, MD, Catherine M. Gordon, MD, MS, SECTION ON ENDOCRINOLOGY | PEDIATRICS Volume 138 , number 4 , October 2016 :e 20162398
 Idea Fitness Journal, June 2018, p.34, “Bone Health, a Primer” by Maria Luque, PhD
 Idea Fitness Journal, April 2018, p.13.; original source: NeuroImage, Volume 159, 10.01.2017, Pages 346-354 “A whole brain volumetric approach in overweight/obese children: Examining the association with different physical fitness components and academic performance.TheActiveBrainsproject” IreneEsteban-Cornejoa,CristinaCadenas-Sancheza,OrenContreras-Rodriguezbc,JuanVerdejo-Romand,JoseMora-Gonzaleza,JairoH.Miguelesa,PontusHenrikssona,CatherineL.Davise,AntonioVerdejo-Garciafg,AndrésCatenah,Francisco B.Ortegaa