As ever, some more info will be helpful.. are you planning to buy new or used? What's the budget range?
Something to keep in mind, too, is that your kids will grow quickly so you may as well look for something that can take 5 adults, plus we always found that for the kids things often went better if we brought along a friend, esp if one child is the only boy or girl, or is separated in age by a number of years... so now you need more space still.
When our kids were young we were fortunate to have a boat that would sleep up to 10 (really!!) and so with two couples, 3 kids and a guest it still worked out OK. Later in their teens we let them take a small overnighter and we 'buddy boated'... that was a neat solution too.
Good luck with your quest.. btw in your neck of the woods in the used market I'd think a Rival in the mid to high 30 foot range might be a fit..
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"