Multiple sports in HS or MLS Next?

I'm thinking ahead a couple years here. But it seems that my kid will have a fork in the road in a few years.

It is my understanding that if you play in MLS Next that you are not allowed to play school sports. (can someone confirm?)

Anywho, so when he starts U13 MLS Next (assuming he would make the team) he will have to decide if he is going to just do soccer or if he will also play baseball (or football/tennis/whatever if he decides). But he played Little League baseball this Spring and...

Multiple sports in HS or MLS Next?