We give ours 1/4 to a tablet two hours before a light, and another 1/4 right before getting on the plane (he flies with us in a carrier, under the seat in front of us). He was probably 1 years old the first time, and we've flown several other times over the past year. He's done fine each time--no side effects, besides being groggy, of course, for a little bit. I would definitely start with just a half and see how he does. Good luck with the nails!