What do your kids like to drink?
They both like fruit juice. But there is a difference.
One child really likes fresh watermelon juice, and the other child likes sweet apple juice more.
So I have to buy them by type. = So I have to buy each type separately.
I think they get jealous if I buy only one of them at home.

This is nice. We can also say this way: 

They both like fruit juice, but there’s a difference. One child really enjoys fresh watermelon juice, while the other prefers sweet apple juice. So I have to buy each type separately. I think they get jealous if I only bring home one kind.