Aside from a brief flirtation with being a family-friendly destination in the '90s, Las Vegas is really geared toward adult visitors and their needs much more than it is for kids. Granted, daytime-wise there are some great pool areas that are very kid-friendly -- check out our list of Top 10 Pools for details about who has water slides, lazy rivers, waterfalls, and so on, plus plenty of Activities and Attractions to keep them entertained. The bad news is that childcare-wise, neither hotels downtown nor the Strip offer any options for guests (some do provide facilities for employees).
So, if you'd like to leave the kids in safe hands while you go out to hit the casino or enjoy a nice romantic dinner somewhere or go dancing, one option is to venture farther afield to some of the "locals" casinos, where excellent childcare facilities are provided and from personal experience we can vouch for the fact that younger kids at least really have a lot of fun there.
The nearest facility to the Strip is at the Palms, with other options at more outlying casinos including Boulder Station, the Orleans (also not too far from the Strip), Santa Fe, Sunset, and Texas Stations, Red Rock Resort, and Loews out at Lake Las Vegas. For complete details of all these facilities, check out the Childcare section in our Visitor Guide, where you'll also find a wealth of other useful information and tips for enjoying your stay.
For children the ages of your daughters, you're looking at $6-$7 per hour each, plus any meals they might eat while they're there.
Alternatively, you could check out the Yellowbook (the former Yellow Pages) in your hotel room and find one of the local services that will send a sitter to your hotel room. It's been awhile since any LVA staffer has required such services, so we can't vouch for any from personal experience, but your hotel concierge might have some suggestions and what follows is a short list of some of the larger agencies we found in town that offer this service (which is a lot more expensive than the Kids Quest-type option):