I think you'd do good with the Bicycle Leaf Backs. On the one hand, they have a Christmas-y look and color scheme. But on the other hand, they're not specifically about Christmas or the holidays, meaning they'd see use in the rest of the year as well.
Otherwise, really, I'd stay away from a Christmas deck altogether. Perhaps something nice and basic but different - Tally Ho decks, Twins, etc.
Of course, you want more variety - the Coke decks were mentioned, there's a modified reprint of the Santa Backs by Bill Merz based off the Maiden Back decks. USPC used to put out some holiday-themed mini decks, though they aren't easy to find - I haven't seen them since maybe the 2012 catalog.
You can also get decks that are like toys themselves. There's a Spongebob Squarepants deck printed in 3-D complete with two-tone glasses in red/blue. Nephews a bit older might get a kick out of zombie-themed decks. USPC has the Cat deck and two versions of the Dog deck - and both also come in minis, though with far fewer cutesy photos in them.
However you opt to go, I wouldn't stick too strictly to "holiday-themed" only. How many kids wear those holiday-themed sweaters between the second week of January and Thanksgiving? Go for something that sparks their interests. Maybe a kid likes Harry Potter or steampunk far more than Santa Claus or some snowmen? Younger kids would dig holiday-themed cards more than the kids at the older end of that age spectrum.
Order quick - remember last year's cruddy weather and shipping fiascos?