Damn. I am no good at advice.
If you've read my old story. Little Trouble Makers, the main character doesn't even know the real meaning for babysitting.
The best advice I can give you:
No bad language
Be entertaining
And don't actually sit on the kid :3
And if this kid is flirty, play along. He's a kid :D
Author's response
Yeah, I wouldn't swear, I don't know why I'd sit on him... I'll do a mickey mouse impression