If you buy really expensive things for your kids when they are growing up, it'll be hard for them if they can't buy those same things when they are adults.
この場合、次のような言い方ができますよ。
ーIf you buy really expensive things for your kids when they are growing up, it'll be hard for them if they can't buy those same things when they are adults.
「子供に高級品を買い与えて育てると、彼らが大人になったときに同じものを買えないと辛い思いをする」
really expensive things「高級品」
when they are adults「大人になったとき」
ご参考まで！
カナダ 
