On the Disneyland website it states that guests staying at the GC can use the amenities of the Disneyland Hotel and the Paradise Pier, so I assume that means you could use the pools at any of the Disney owned hotels.
There have been conflicting reports on this. At one time, GCH guests could use the Neverland Pool. When we stayed there last June however, I asked and was told no. The pools at both GCH and DLH are surrounded by large iron fences with a locked gate. The gates are accessed by your room key. Just to see I tried my GCH key in the DLH pool gate one night on our way to Goofy's and indeed, it did not work. While I love the DLH and the Neverland Pool, your kids will not lack for pool fun at the GCH. It has a lovely pool area with a fun slide. It also has Whitewater Snacks which is a great place to get burgers, salads, sandwiches, nachos, etc. They have waitstaff that circulate for food and drink orders or you can handle that yourself to save the tip. I would tell your kids no dice on the Neverland Pool and then see what they say when you check in. If they do somehow allow your key to have access to the Neverland pool, that will be a nice surprise, if not nobody will be disappointed!
I also agree with Amy&Dan. The Neverland Pool has a cute theme and all, but in all reality, the pool and slide is not any better or more fun than the other pools/slides at the GCH or the PP.
Our kids had a WHOLE LOTTA MORE FUN using the pool and slide at the Paradise Pier than they did at the Neverland Pool. Plus, the Neverland Pool was cold when we were there. I just couldn't swim in it because it was too cold. However, the Paradise Pier pool was nice and warm.
I don't know.....I just don't think it's worth the trouble to walk all the way to the DLH from the GC just to swim in the Neverland Pool, especially since there's an awesome pool and slide right there.