Ordering toddler shoes online sure beats an in-store meltdown. But, “not getting your child fitted properly is doing them a big disservice,” warns Manhattan podiatrist Dr. Elisa Kavanagh. As a family doctor (and mother of three), Dr. Kavanagh has some helpful tips for your next Zappos spree.

Don’t guess your child’s foot size. Instead, have him measured at a shoe store—or buy your own sizer (Squatchi is great for US sizes and we like pediped’s version for European sizing). Dr. Kavanagh advises going up a half-size to allow for a half-inch of space (about a thumb’s width) between the tip of the big toe and the front of the shoe. This offers room for comfort and growth, but not so much excess space that your child will be tripping over her own feet. Keep crawlers in bare feet. “If your baby’s just crawling, she shouldn’t be in shoes at all. That’s weighing her down,” says Dr. Kavanagh. She describes infants’ bones as being “malleable as butter,” explaining that putting them in the wrong shoes early on can interfere with their development. Save the soft soles for cruisers. Once toddlers are on the go, it’s time for something more substantial. Look for shoes that offer ankle support (like little booties) and fit snuggly with laces or Velcro. “Babies tend to walk on their toes, and providing them with the right structure encourages them to get their heels down,” she says. Opt for leather. “Full leather can stretch and isn’t as restricting,” explains Dr. Kavanagh, who also suggests looking for a shoe with a sturdy but flexible rubber sole. Remember most babies and toddlers have wide feet—a rounded toe will work best, she says. Buy from a site that makes returns and exchanges easy, as there’s no substitute for feeling how the foot fits in the shoe itself. And finally, don’t get too attached to cute kicks: according to Nordstrom’s shoe experts, kids’ feet grow an average of a half size every three months (!)