Thanks for all the suggestions, though I'm not sure anyone came up with the magic perfect answer, but some interesting prospects.
A few thoughts back: we've been to the Gulf Coast side of Florida a fair amount, as well as Orlando. I'd like to visit the Miami side but one thing I was looking for was the ability to actually go in the water, not just walk along it in a sweater, in February-ish. That said, I'm always intrigued by the Miami-area reports by VI and others, it'll happen one day.
New Orleans is the most obvious place in the US I've never been, but I'm just not so sure about the attractions of either NO or Miami for small kids.
Dees_1, I've been looking for another spot in Mexico that would work for the kids and have yet to really find it though it must exist. One book at least said Zihautanejo/Ixtapa was NOT especially kid friendly, not sure why. Also the calmness of the Caribbean water at Playa is important for small kids.
Vancouver etc. would work at another time of year, I appreciate the suggestions on that. Hawaii, I just don't think we could handle the flight yet. The 3/almost 4 year old is a pretty energetic guy, he could maybe go 6-7 hours but not 12-14 on a plane yet. Though volcanos are a big, slightly scary selling point for them.
Ireland we actually visited about a decade ago and had an absolutely wonderful time. That was what had me thinking about Scotland (well, that, and
this movie). They're not as obvious as a beach when it comes to things that would keep a small child interested, but stay at farm B&Bs and it could work.
So, thanks for interesting things to think about. Here are a couple of direct questions if anyone has any answers:
• Any recommendations among specific Caribbean islands (besides Jamaica, noted) as having both great beaches and interesting food/culture? One I was looking at was Curacao, for instance.
• Spain and/or Portugal. I thought that might be a doable corner of Europe for the kind of vacation I'm talking about, albeit still sweater weather I assume.