I heard that washing the plants in a very weak bleach-water solution, it kills snails and algae on them.
Of course, then you'd have to be very careful putting them back in your tank. You'd need to wash them and soak them and wash them a bit more.
If they're only on one or two leaves, would it hurt just to remove those leaves?
Fortunately, I haven't had an outbreak of snails yet in any of my tanks. I heard the bleach trick when I bought plants online, as they almost always have unwanted critters
Good luck with the snail issues, and of course your fry!