Since you're as likely to be photographed on Christmas morning as you are at Christmas dinner, it's important to put forth a little bit of effort and make sure you look mildly presentable as you post with your son or nephew and his sweet new lego set. In my opinion, the best way to achieve this is to wear at least one piece that's not actually pajamas.
I think an inexpensive flannel shirt from Old Navy or Target is the perfect partner for leggings and flannel pants, as is your trusty chambray shirt worn over the tank top you slept in. (Pro tip: For extra butt coverage, pick up a non-ruched maternity tank that will act as a knit dress of sorts)
Another option is to pull out a pair of your favorite running tights or yoga pants, since they're much thicker than your average pair of leggings, but wear them with a long non-pajama tee or button-down and a cozy cardigan. Easy, right?
Need more ideas? Here are some similar ideas from holidays past: