My husband is a Physician's Assistant in a dermatology office and all of us have very fair skin so I'm pretty good at putting it on all of us and I know if any of us get burned I will hear about it from my husband. For myself (and the kids), I like the continuous spray sunscreens because it's quick to put on and you aren't spending a lot of time rubbing it in. So, I can spray all of us quickly and move on. My son is 4 and has never been sunburned and thankfully I can say the same for my daughter, Nicole (who has OCA). And, we live in Florida and are outside a lot so it's a miracle that we aren't burned all the time.
As for reapplying, my husband says the sunscreen companies will tell you 4-6 hours but he recommends every 2 hours especially if you're swimming or sweating a lot.