OK, this is getting serious now.

1. Play with your hair.
2. Play with his hair.
3. Definitely whisper in his ear.
4. Maintain eye contact, but drop them every now and again as if you're embarrassed.
5. Grab him by the back of the neck when you kiss him goodnight.
6. Sigh through your nose.
7. Wet your lips, often. Leave your lips slightly apart after you wet them.
8. Run your fingertips along your lower lip, while they're slightly apart.
9. don't talk about the kid (you'll distract him with filial responsibilities, and he knows you're not bothered by it already).