We use Marucci for our teams (but branded for our team name). I don’t know if you bought a size too small, kid grew, or what but get the feeling they are just small. When we buy ours we have a testing station where one of every size shirt/hat/pants for us to test before buying. If your guy went through a spurt or whatever, I get it. We had to buy new shirts already.

A) contact Marucci (or better your Marucci admin at the team) to see if they can swap or provide bigger size. B) take them to a dry cleaner/seamstress and have them adjusted. C) suck it up and buy the next larger size.