You don't have to smile.
Think about some of the most powerful images you've seen, the really good ones that move you to a different spot: I'm betting the biggest images are the ones where the subject isn't smiling.
We we had a goodnight tonight. We had bubble baths and book reading, followed by a bit of tv in bed. But the I told him it was time to go to bed..
Grab those moments. They're the ones that you'll look back on and laugh. At least I hope they do.