For your sitiation something like:
How's my favorite little brat doing?

or
Hey, what kind of mischief you gettin yourself into these days?
Those would work for anything, but others could be:
- Made you look
- I'm luring girls to my house with candy, which do you prefer skittles or M&M's?
- Aliens are coming to abduct all the good looking sexy ass people! you will be safe, I'm just texting to say goodbye.
- Hey princess, I just came back from the aquarium and I saw the cutest fish there...it reminded me of you =P
- You just popped into my head so Hi...now please stay out of there.
There is a topic somewhere on here about texting openers. Hope I helped!