High on Water
"I tend to think dental sealants are a bad idea"
You'll be doing more for your five year old to teach him to swish water around in his mouth (to rid his mouth of excessive acid) after every meal.
It will be much easier then, once he gains control with that practice, to put good things in that water (like Iodine
for natural remineralization of the teeth which would be impossible if they were sealed).
It will also be easier to introduce him to OP, once he learns how to swish water around...I daresay that, as a five year old, he can swish liquids around in there quite easily already! (And squirt them out, too!) ;-)
I do hope your drinking water has no fluoride or chlorine in it.