: I've never fiber glassed before. Do you think it would adhere to
: the plastic?
Not very well.

:Would the fiberglass be likely to crack at the
: transition between the wood and plastic?
If the plastic is not flush with the wood surface, you'll need to make some sort of fillet, or you'll probably get voids.

: I know that when you
: put the fiberglass over wood you basically can't see it. It is
: clear and you can see through it to the wood. I assume
: fiberglass on plastic would also be clear, but would it distort
: the view too much?
Make up a small panel and try it out; my guess is that you will find that the fiberglass is not uniform enough to give you a 'clear' view.

: What do you think?

My choices would be:
Polaroid sunglasses to cut down on surface reflections
Some of the cheap inflatables have 'windows' (as I recall)- might be an easier alternative.

Also, are your kids paddling where there is a lot of 'stuff' to see underwater? My recollection of swimming/snorkeling in freshwater as a kid is that there wasn't a lot of action underwater. Lots of starfish and other goodies in the ocean here , though.