Swimmers should have 2 pairs of goggles - one for practice and the other for racing. The goggles worn for practice should be very comfortable and not fit to tight. Racing goggles should fit snug to prevent them from falling off during a start.
Goggles fit properly when you press the lenses over the eyes without the strap on and they stay on, if not then look for a pair with different lense size or nose piece size until they are comfortable. If the retailer does not allow you to try the goggles on it is recommended you go to a retailer who will. Goggles are an expensive but important piece of a swimmers equipment and should fit properly, just like a hockey player and their skates.
Most goggles have anti-fog coating but it does wear overtime. When this occurs a swimmer can lick the inside of the lenses to prevent fogging. When choosing goggles for indoor use choose lenses colors which are light (clear or yellow). Try to avoid lenses that are too dark (dark blue and black) this inhibits the ability to see clearly in the water, which could cause accidents. Many types of goggles have straps and nose pieces which are sold separately and make repairing rather than replacing an inexpensive option.
There are a variety of cushioning options for around the eye portion of the goggles, the silicone gaskets are the safest because they are hypoallergenic. Make sure that the silicone cushion fits snuggly around the lenses of the goggle. This is a common reason for leaking goggles.
For those swimmers who require prescriptions there are a couple of options. A swimmer can now purchase prescription goggles from a few retailers. The other option is to wear contacts with regular goggles. It is recommended that swimmers who are competiting should wear disposable contacts at competitions. If the goggles fall off during races they will not be faced with loosing expensive contacts.
If you go to a retailer who specializes in swim equipment they will also guide you in choosing the proper goggles for your child. Remember to have your child with you to try them on until they find a pair they like then take that pair with you.