question. there is organic play and then there is specialized sports. where do you cross the line? >> unstructured activity is probably -- will lead to less of these overuse type injuries that we see. it's not until you introduce a parent or a coach into the activity that it leads to these overuse type injuries. >> reporter: it's one thing to encourage babies to stretch and roll, say psychologists like wendy walsh but toddler sports training is extreme parenting, she says, especially for kids who may not be ready. >> you want to be a good parent? go to the playground. climb the monkey bars with your kids. you can get in shape with them. i used to do pull-ups on the bars and sit-ups in the sand box. that's what kids need. >> reporter: the mayo clinic concludes unstructured physical activity not training is what is best for kids up to age 5 but tell that to a thriving gym full of 2, 3, and 4-year-olds. >> i understand there are skeptics and there are concerns and every good thing can be done in a harmful way, but the fear