Tickla,
I have to put my two cents in here: I too, have three kids (oldest is 15, others 13, 10) and we have taken our pup to FW 3x now (and tented before that).
You will love being up off the ground-the first time it rains you will smile to yourself in your sleep!

We have a 2005 Jayco 12HW which we pull with our minivan. There are several things to look for when buying a Pop-up (pup for short): how will you use it (state parks and FW only or do you want to roll it back into the woods and run off battery), who will use it, and what do you need/want?
For your 3 boys plus you and your spouse, you want at least two beds and a dinette or couch (gaucho) that will convert into a 3rd bed. We have the potty/shower combo in ours which helps with those late night "emergencies" so you don't have to step outside late at night (never used the shower in it).
We like the fridge we have in our Jayco so we can buy groceries and eat our meals at the campsite at FW (we pack a picnic lunch most days in the park and splurge on one in-park meal during our trips-feeding 5 (the kids eat like horses) at WDW can get pretty $$$$$$

)
PM me if you'd like to ask specifics about a pup (or anyone else). New or used, it is a great way for a family to spend some quality (and quantity) time together with nature ( and Mickey).

Go look at trailers at dealerships, go to RV shows, and talk to people. I keep a log and we've spent 95 nights in our pup in 3+ years and it's my cabin in the woods, my condo at the beach, my time share at WDW, and best of all it's PAID FOR
Bama ED