I'm sure you should have in it who you would want to take care of your children if all their parents die.

Other than that, I guess that children will by default inherit (after any spouses, before anyone else) your estate. Though of course you could state in your will how much of your estate goes to exactly who.

My parents had adult children (my step siblings) at the time I and my brother and sister were still at school. During that time they had provision in their wills to provide for the education of any child not yet in adulthood at the time of their deaths. Now that all of us are well and truly grown up, that part has gone from their wills, and they will just split everything evenly between the 6 of us.

TBH it's probably something to consult a lawyer about (and I am most definitely not one of those).