When playing how rough is to rough?

Now that my Kitty's have gotten to know each other better they've started playing or at least I hope thats what this is. Cinnamon (11 month) is wrapping her little paws around Bell's (9 weeks now) little middle and starts biting at her neck and batting her around Bell just kinda falls over and lets her do it she doesn't try to play back much but if cinnamon walks away Bell does try to follow. I'm assuming they are just playing since Bell isn't afraid of Cinnamon and never cries when this is going on. I was just wondering If this play is to rough for Bell She's still a little thin and pretty small (but we're working on that now that now that the vet has wormed her) I don't want to intervene to much between the two because I'm hoping Cinnamon will be able to teach Bell the things her mother didn't have a chance to and that I can not. She's already learned some from Cinnamon when I brought her home she never cleaned herself or played with toys or even used the little box. But now after watching cinnamon do these things a tie or two she's using her litter like she should, She's eating and drinking from a dish, and trying her best to play with the toys and has started grooming herself (with cinnamons help who sometimes decides that she's not doing it fast enough so she gives her a hand). So I really don't want to step in and interrupt them if everything is all well and good. They seems to be bonding little by little and I would like to see that continue. But I don't want Cinnamon to get to rough with Bell and accidentally hurt her. I separate them when I'm not home (bell has a comfortable little room in our bathroom that she doesn't seem to complain about.) and only let them together when I am able to supervise but was wondering if this kind of play is okay? and when to intervene if I need to? I've never had two Cats at once before so Kinda new to this stuff.

i have exactly the same thing - we got a new cat of same age & sex & they soon started doing this. i think it is playing cuz as you say - no noise or anything. feliway diffusers seem to calm it a bit, but every now & then they have a ruck. it often starts as grooming eachother, so i've always assumed its good!! i stop it when yoshi, the gentler of the 2, starts to look a little bewildered, i think she gets fed up with it after a few mins.

i'd say probably just monitor it closely until little one is a touch bigger.

Sounds like normal playing/teaching, in my experience the kitten will cry out if they are hurt.

Yes, quite normal. Cinnamon is a good teacher. I don't think she will purposely hurt Bell.

Thank you all very much, since yesterday Bell must have picked up on what she's supposed to do because she seems to be playing back lol, before she just kinda laid there but now is pawing and biting just the same and sometimes is initiating it. Bell seem ti tire of it faster and will give me a little meow when she's done so I put a stop to it for a min, but after taking a few minutes break they go right back to it. lol

I have that with the oldest brother and sister. Except he's sneaky about it, he puts his front leg over her shoulder and starts washing her (which he doesn't mean to at all, he's sets her up for a false sense of security) then he goes in for the kill and starts biting and trying to wrestle her which always leads to her spitting, growling and running away.