Rant: Why do kids clothes shrink SO FAST?

I swear my 7yo just wore these pants last week and now they're capris. I feel like I'm constantly buying new stuff. And don't even get me started on shoes - how are we spending $80 on sneakers that fit for like 6 months?? Is this just the cost of having kids or am I shopping in the wrong places? Someone tell me there's a hack I'm missing because this is killing my budget.