The FA will move people to put you with the two year old, they are not under any such obligation to do so for the five year old, That's the way it is, get over it. if you do'nt like it, then drive. People think nothing of putting their kids with strangers in day care all day while they are many miles away, yet it's a problem to be three aisles away in a plane? Sheesh!!!
Frankly, I won't give up my aisle seat for a five year old to sit with a parent. Get there early, get up in the middle of the night to print your boarding pass, do everything that I do to make sure I get the seat I want. Take responsibility for yourself and your kids, don't try to inconvience me because YOU neglected to plan ahead.
Anne