Hands off Please

My boyfriend is about the only person who can touch me without putting me in a horrible mood.

Well now his kids are doin it . They don't ask, even though I've spoken to them about personal space. The nine year old in particularly bad about the random touching because she at eye level with my tummy and it's not one kiss no she's one of those who thinks its cute to give you a thousand kisses and is always touchy feely especially when she's tryin to get away with something. She's done it to me in public twice already and I've bitten my tongue.

Now her sixteen year old brother is doing it and I about blew a gasket when he kissed my tummy out of the blue. As much as I love my step son, I've caught him looking at me in a not so childish manner. His father has spoken to him about it and so has his grandfather. I don't want  A man child kissing me anywhere that isn't on the cheek. Even then one kiss is enough as he doesn't always seem to understand that I'm the adult. ( @ 6'1, 260 lbs, he's physically a lot bigger and he thinks that makes us equal.)

How do I get the point across and get my boyfriend to understand my discomfort without making him offended. He's super touchy about anything to do with his kids and I'm so sick of this situation that my temper is about to blow.

Help!