Concentrate on any pressure points you feel as you walk around; they will only lead to problems with extended wear. A padded tongue and interior padding around the ankles can improve comfort.
If you're buying hiking boots for a child, avoid the temptation to select shoes a size larger than they need with the expectation they'll grow into them. Boots that are too big are a major cause of blisters.
More: What to Bring on a Hike
Break Them In
Your "shopping" shouldn't end when you leave the store.
It's important to break in your new hiking boots slowly. Put on your hiking socks and wear your new shoes indoors for a couple hours at a time. You'll want to return them for a new pair before your next hike if they aren't the right fit.
If they still feel good, make sure to take one or two day hikes in your new shoes before heading out on a long, multi-day backpacking trip.
By making the right choice and caring for your new shoes—by keeping them clean and dry when you're not using them—you should get miles of happy hiking out of them.
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