I think you'll need 75-100 pts to stay every other year in a 1BR. You could start with 75 and borrow some points for a few years before adding on, or if you buy resale you might get a contract with banked points. I'd buy 100 pts if you can, though. With only 50 pts I think you'll have to shorten your stay to Sun-Fri to go every other year.
We have three kids and we are in the process of buying an OKW resale contract. We just received our closing docs so hopefully we'll be official in a few weeks. I ended up choosing OKW because they are supposed to be adding a sleeper chair to the villas so a 1BR will officially sleep five, they are the roomiest of the
DVC villas and the OKW units are pretty much the least expensive point-wise and resale prices are among the lowest. I always love a bargain and we don't want to spend a huge amount of money on DVC right now. I also like the condo style layout (parking at unit) and that OKW looks like a peaceful retreat from the busy parks. Everyone's personal preferences are different, of course.
One thing to keep in mind is that as of now you are allowed to book 5 people in 1BRs that officially sleep four. AKV (except value 1BRs) and BLT 1 BRs sleep five and as I mentioned they are supposedly changing OKW to sleep five. I've read that DVC does not provide towels and linens for the fifth person in a villa that officially sleeps four, so you'll have to bring sheets for a blow up mattress and share or pay extra for another set of towels.
As for most fun with kids...the BCV pool area is very popular, but all of the DVC feature pools have slides and look fun to me. Some of the pools have zero entry which is nice for little ones. We've stayed on the monorail and it is great being so close to MK, and BLT is on the monorail. You can walk to EP from BCV and BWV. AK has the animals. I would find a website with pictures of all the resorts (like allears.net) and see what looks like the most fun for your family, and remember, children grow up too quickly so keep in mind what looks fun for older kids as well.
Hope that helps a little!
