I find that the spray doesn't last as long. How fair are you and your kids? We are also a family of 4 and although my son and I do not burn easily, hubby and DD burn VERY easily as in DD never goes outside to play without sunblock. We are planning on about a regular sized bottle of Coppertone Waterbabies (either 50 or 70, whatever I can find) PER DAY OF DISNEY! Plus face sticks-I'll probably bring 3. I've started buying them already although our trip is not for another 34 days. Coppertone has coupons on its website ($1.00 off) and I look around for the sales. My plan is to buy 2 bottles per weekend until the trip. If I have extra I know I will use it since we are at the pool and beach all the time anyway.
That was a long answer to your question...but NO I don't think it is enough if you are fair skinned and burn easily and plan on reapplying at least once or twice a day. Better safe than sorry. Nobody wants a painful burn in the most magical place on Earth!