Just some thoughts from an old couple that has been through it ...
I can see why you might not want to be traveling around a lot with the young ones, and a weekend getaway would be just the ticket. But instead of parking a brand new unit at a seasonal site, why not look to see what is already for sale at the campground where you are looking?
There are usually units on desireable sites for sale. Somebody else as already taken the big depreciation hit, and spent the money on blocking the trailer up, installing a screen room, building a deck, etc. Often, the unit was a "park model" or "destination trailer" to start with, which both have numerous features that you don't get with a TT that has to be ready to run over the road.
After a season or two, you will have a much better idea what the family likes and can trade up accordingly ......