Second

Wow, I just realized that this year will only be Laurel's second Christmas!

She was born two weeks after Christmas, so even though she will be three years old in less than a month, she hasn't been around for that many actual Christmases.

It's Isaac's seventh Christmas, even though he is six years old.  He has plenty of experience.

Edited to add: Okay, my math expert says this is just not true.  This is Laurel's third Christmas.  She was born in January 2009, so she celebrated Christmas in 2009 and 2010, and 2011 will make number three.  I guess I can't add.