Just because a baby isn't complaining doesn't mean his/her shoes fit the way they are supposed to. Here are some simple visual cues and fit tests that podiatrists recommend. Leave about a thumb's width of wiggle room between the front of the shoe and the longest toe for a comfortable fit. You should also be able to easily slide your index finger down to the second knuckle between the heel and the back of the shoe. If it's too tight, choose the next size up. Put socks on baby's feet while shopping for shoes if he or she will typically be wearing them while wearing the sneakers. Then do the same fit test above. Be on the lookout for signs of irritation. Redness is a telltale sign that shoes are either too tight or too loose. If toddlers are always wanting to take one or both shoes off, that could signal that they are not comfortable. Keep in mind that unlike adult shoes (ahem, heels!), there should be no "break-in" period for baby shoes. They should be comfortable immediately.