When you are buying toddler shoes, each shopping trip should be treated like the first -- examine all aspects of the shoe and make sure it fits all around. Kids’ shoes are different from brand to brand, style to style, and sometimes even from shoe to shoe, Cox says. So the "trying on" experience is important.
There are three key areas of the foot that you should focus on when buying toddler shoes: the front of the shoe, the back, and the width. All three will play a part in whether or not the shoe fits properly.
Finally, follow one last simple test when buying toddler shoes: Ask your little one to walk around in them. You don't need to worry so much about the style of the shoe. Instead, think about whether it looks comfortable and fits well."
I find it very easy to buy toddlers shoes online - sizing is easy as you just pull up the sizing chart on Amazon and pick what size matches closet to your child. There is also sizing by European method and you can also size by inches and age (I have included the US Robeez shoes sizing chart below for easy reference) I bought Zachs Robeez just a little big because I want him to get some wear out of them but not too big because I don't think it's good for kids shoes to be too much bigger than their feet.