My boy will be 8 in a month or so. We've been watching "American Ninja Warrior" and he's really impressed at watching people work out and train in gyms.
When I was a pre-teen (10-11) my parents got me a chin up bar.
Since he is under 10 and still developing:
Q: Should I wait to get a chin-up bar or is it safe at this age and it won't affect his physical development?