Suit
A training suit (twenty to forty dollars) is the right buy for ages 5-12. Tech suits are for kids who compete year-round at age 12+.
Polyester lasts longer than nylon in chlorine. The brand on the tag matters less than the fabric.
A snug fit. Not painful, not loose. Loose suits create drag.
Goggles
Press the goggle to the eye socket without the strap. If it suctions for two seconds, the seal fits.
Anti-fog coating wears off within a season. A drop of baby shampoo on the inside of the lens is the workaround.
Buy two pairs. One always lives in the bag.
Cap
Silicone is more comfortable than latex and lasts longer.
Long hair: a longer cap or two caps stacked.