Choose a flattering frame. Pick a squarish one for your round-faced cherub, a round shape for your angular angel. And shoot small: Oversize glasses can make a kid look bug-eyed.
Be flexible. You may think plastic styles are cuter (bright colors, fun shapes), and they're fine. If you can't get a good fit, though, metal's easy to adjust, says Dana Cohen, a pediatric optician in Medford, MA. Look for flexible titanium and spring hinges, which bend without breaking as easily.
Focus on the bridge. A too-tight nose pad will pinch and prevent the glasses from sitting close enough to your child's eyes. When it's too wide, the frames slip and slide. You'll know it's right when there's very little space between your child's cheek and the lower rim of the frames.
Ear this. For a child under 3, go for a silicone-covered, wraparound earpiece. For a baby, consider a soft strap that fits around the back of the head (otherwise, good luck keeping them on!).
Opt for safety. Polycarbonate lenses are the most impact-resistant. An antireflective coating will pad the price tag but usually results in sharper vision by letting more light hit the retina.
Read all about it. If your kid's resisting wearing her specs, pick up Luna and the Big Blur, by Shirley Day ($9.95), about a little girl who ditches her glasses and then does silly things like putting ketchup on her ice cream. It'll make the benefits crystal clear!