We have been to WDW during the 1st week of Feb. for each of the last 4 years. DSs were 1 and 3 for our first trip. Everybody is correct that the weather is quite variable at that time. We wore jackets, sweatshirts, hats and mittens one year because the temperature was in the 40s (30s at night) and it drizzled most of the time. We did see people swimming in the pools on that trip but we didn't. This year, it was sunny and 80, 70s at night. The other 2 years were in between. Layering clothes does work best.
There is only one water park open during that time because the other one is down for rehab. I think the park open each time that we have been is Typhoon Lagoon. I can't recall Blizzard Beach being open, and River Country appears to be permanently closed.
With small children, you do need to make PS arrangements for any sit down restaurants so that you don' t have to wait long. The buffets are great because you don't have to wait for your food. I wouldn't do 3 sit down meals a day with young children. I would plan to eat counter service at least once a day. You will need to call for Cindy's on the first day that you can. You can wait until closer to your trip to make your other PSs but don't wait too late if, for example, you have your heart set on Chef Mickeys at 6:30 on Thursday.
The great aspect of an early Feb. trip is low crowd levels. The year that it was cold and drizzling, we walked onto every ride. On our other Feb. trips, 20 minutes has been our longest wait (we do use the fastpass as much as we can).