What is normal behaviour between siblings?

[Gargula]

I have a DS nearly 3 and a DD 7 months old.
At first DS was very good with his sister, lots of gentle kisses etc. But recently he has become a bit more "over the top".
He always seems to be in her face, kissing her hands, feet etc, pulling her around, picking her up (trying to!) and pushing her down, and he'll always snatch toys from her. Sometimes when she pulls his hair he will hit her
I must admit I have not been brilliant with this as it drives me bonkers. I've started to put her in a playpen to protect her but he tries to climb in, drop things on her etc.
So is this normal and what can I do about it?

Thankyou homeboys
I think you've hit the nail on the head with the jealousy issue. I feel so guilty that he does not get as much time as he used to, and I suspect that my behaviour is at the root of the problem (DD is very loving and clingy with me and I don't discourage this)!
I do try to give him more one on one time but DD only naps 30 mins at a time.

sounds normal

and ime normal is anywhere between utter adoration and attempted murder, swinging from one to the other in seconds and hitting all the steps inbetween.

To begin with, babies do nothing. But at 7 months I imagine she's sitting up, rolling/crawling, grabbing HIS toys and playing with stuff HE wants to play with, or playing with HIS baby toys and not sharing her things with HIM.....can you see where this is going?

She's starting to encroach on his territory and he doesn't like it. And he's jealous.

My key tips are asking the older one to 'help' you and telleing them how much the baby likes them because they're so big and clever, and when the older one inevitably wallops the younger one, don't tell teh older one off (ignore them completely), just pick up the victim and make a huge fuss of them.