You already have kids together!! Marriage is the easy part!

I felt no different the day after I got married and didn't really even feel like it was that big a deal. I adore my DH and I'm very happy we are married but really it doesn't change much.

The prospect of having a child with him is so much more daunting and definitely permanent. You've already done that, so whats the fuss? Since you already have kids together, you're already bound for life regardless, so your marriage is just a beautiful, symbolic act and an excuse for a bloody good party. Enjoy it!