Should kids join exercise programs?

Kealey 🚨👮🏼🍝🏳️‍🌈🇨🇦 • Demi- Pansexual • wannabe randi • meatball head • Ex- Jehovah's Witness • Pro-CHOICE • pro-drugs • GAD & Depression • 16 years old • Polite Canadian until you piss me off •
I do crossfit and at our gym we have kids fit (4-12 I believe). I am an assistant coach and think it's such an amazing thing for kids to do! 
What are your views on having kids exercising?