My DD who just turned 6 had her first optical appointment a few weeks ago when school let out for break.
It was a very thorough test, which I really appreciated.
First she looked through the focusing machine, don't you love my technical term?! It was a picture of a farm that automatically measured the focus of her eyes.
Then they tried the puff in one eye. She didn't like it, so they didn't push the second. She then read the letters on the eye chart, then based on all these findings, her eyes were dilated. Then the focusing farm test was repeated and the doctor looked at her eyes through various lenses.
Turns out she's a +3.0 in each eye. I got her two pairs of frames, figured with a kid two was better than one! The doctor recommended polycarbonate lenses, they are more durable but also lighter and thinner. Regular lenses would be highly magnified, like the "coke bottle" glasses. I really was shocked by the cost of glasses!
She's been wearing them about a week now and is doing great.
Good luck to your little one. They will do fine!