Hmmmm this ought to be good. Please ping me to an explanation and we will need photos, too.
Well, back from shopping...
Santa pants are jeans for each family member which are wrapped and addressed as "from Santa". This sounds dumb, but it's complicated. See, we didn't 'do' Santa, until my littlest brother, who has Down Syndrome, went to private Catholic school and they told him Santa would be bringing presents. So he got so excited and wouldn't believe us that Santa doesn't... anyway, that year Santa showed up with gifts and all, and what the brother got was pants.
So to reinforce the idea that the presents are really from Mom and Dad, from now on we say "Santa brings pants" and hand out Santa pants. It's a lot of fun and a good way to get a new pair of jeans.