At least it's Feb - temps not too bad by then - say, mid 70's?
My brother has lived in LV for about 10 years now and hates it with a passion. It's certainly one of the least child-friendly cities in the US. Sure, there are a few things to do on the Strip that are allegedly child-oriented - look at the lions in MGM, gawp at the animals at the Mirage (are they still there after one of them tried to eat Roy?), the M&Ms 'attraction' (expensive and essentially a big advert for buying their chocolate), watch the volcano erupting outside whichever casino that is, lots of the casinos have evening 'events' outside their pitches to draw people in. And so it goes. The pools outside are good, but don't expect the casinos (where you'll probably be able to get a good hotel deal) to put on a lot for young children. They want to keep kids out of the casinos!
But it's horribly over-stimulating for a three year old, and though it's one of the cheapest places to eat and sleep in the US, money has a habit of being spent there...
Sorry, can you tell I hate the place? There's an upside - if you have a car or get a taxi, you can drive to the Red Rock state park, about 20 mins off the Strip, and another world. Lovely rock formations, gentle, signposted walks, a visitor's centre with local tortoises. And Valley of Fire state park, the other side of the city (but more like an hour's drive out) is fantastic - great petroglyphs (rock art) of people, animals and handprints for children to spot. And Boulder, a small and cute town a few miles away, is worth a visit for the peace and quiet, and fab 50's diner with great milkshakes!