The family may want to meet the children but I doubt a very young baby cares either way. On a recent flight back from CTA a baby was literally howling the entire way quite obviously in a lot of distress. Granny may have wanted to meet him but would she have if she'd known the 4 hours of torture the baby was going to be put through to get there and back?

Once children are a little older I see no problem with them in any class assuming they're supervised correctly. Annoying people of any age are annoying in any class.