I agree with others in that putting a lot of value into the extra 25 years is not the best idea. I don't know about you, but trying to plan out what is going to happen in 25 years from now is a fool's errand. Way too many things can happen. Heck, the likelihood of anyone keeping their contract for 25 years is highly unlikely. I don't know the numbers, but I'm confident in saying that it is probably less than 5% overall. The resale market exists for a reason -- lots of people sell their contracts at some point.
Regarding your children -- how old are they? If they are still living with you, I wouldn't worry about trying to buy something now that might also work when they are grown and have kids of their own. Again -- that is so far down the road, it is pointless to plan for it now. If your kids end up having kids, you can always buy in at another resort down the line. Sure, prices will likely be higher, but you'll have a better idea of the wants and needs of everyone. Right now, you'd be stabbing in the dark.
Regarding what resort -- don't forget to look at
point charts for each resort. Two lake view rooms at poly for a week will cost 300 points for adventure season and 540 points for premier season (easter and christmas). Conversely, you could get 2 studios at boardwalk for 215 points (adventure) and 376 points (premiere). In other words, poly rooms are about 40% more expensive just on the amounts of points they use. So not only do you spend more initially, you'll be spending more per point.
A 2 BR at BWV would cost 269 points and 477 points, respectively. This is still cheaper than the 2 studio option at Poly, and you'd gain the additional living room, kitchen and in room washer/dryers. Both are excellent locations.
Also -- if you owned at BWV, you could have a shot at the "standard" rooms (they can be very difficult to book even at 11 months, so you can't count on getting them), and these would give you even more value. 152 points for two studios for a week (half the point cost compared to Poly) and the 2 BR is 220 points (poly 37% more expensive).