Return or keep clothes for later

So my son wears 18m clothes and today I went shopping for him to buy summer clothes for vacation.So I bought 24m thinking it will fit him.

So I tried one pair and looks baggy on him so it is big.I bought 11-12 outfits so I’m thinking they will all be big.

But now I’m not sure should I return it and buy for 18 m or keep it for later and still buy new ones?

What would you do ?