In the winter, it can seem like you need an extra 20 minutes to get in the car considering all the time it takes to put on the cold-weather extras. Boots are no exception. Trying to put winter boots on a toddler is something like putting a cat in a bathtub. The effort is exhausting.
If the boots are too small, you're going to have an even harder time putting the boots on, so buy the correct size. One of the most important things to consider when buying boots is that children will most likely wear at least one pair of thick socks along with the boots, which can make boots that seemed to fit in the early fall too small in the midst of winter. Take a pair of thick socks along when buying boots to ensure proper fit.
Your position relative to your toddler can help get the job done. If your little one has relatively good balance, try putting the boots on while he's standing up, letting him hold onto your shoulders for balance. You can then encourage him to push down into the boot to get it on. If you want to put them on him while he's sitting, you'll find it's easier to squat or sit behind him, pulling the boots on as though they were your own.
Of course, toddlers are all about independence and yours may insist that she should be allowed to put her own boots on. Encourage this, but plan for a bit of extra time. Stand back and gently ask whether she'd like some help if she's struggling. If you're relaxed, she will be too.
The style of the boot can play a big role in how easy it is to put on. Look for boots that open up, either by zipper or hook and loop tape. When open, the boot slips on just like a regular shoe. Placing a plastic bag over his foot can also help the boot slip on more easily. This has the added benefit of providing an extra water-proof layer for those days when he's playing in the snow for extended periods.