a day, but getting into more ruins and seeing more stuff I'd say 2 days, especially if your kids need breaks or naps. Definitely bring a kid carrier if you have one. Your kids can do the ladders, it wasn't too bad. Mesa Verde is super cool, the big ruins are so impressive. Some of the smaller sites are really interesting, like at the Far View site there are some places you climb through and play in the ruins a little and an old resevoir they built. I'd say see as much as you can.