3 month and 8 month old kittens play fighting?

So I have an 8 month old kitten called Cass. She's desexed, and a very shy DSH who can become irritated easily. But she's affectionate and loves napping with/on people or company she trusts. It takes about 24 hours for her to be comfortable enough tonal on friends who stay over. We've kept Cass in our current place for less than 4 months now. 

Two weeks ago we bought Beatrice, a beautiful ragdoll/himalayan who is almost 3 months old. She's super affectionate, playful and nudges you for pats and cuddles. They're both loving, good-natured cats.

Since we got the new kitten, we've been introducing them by the book - safe room for Bea, planting her scent in the house, feedings near the door, site swapping, and eventual visibility office other. We've only just started feeling comfortable letting them roam the house around each other, but the progress is very good. We can feed them next to each other, and they're very happy to do that, and they sniff each other a lot and boop noses. They like playing with toys around each other. 

Play fighting is just the problem with these two. It always starts well, and both chase each other around and swat at each other and jump on each other. Cass is learning how to back off, so they're understanding the others limits. But their fighting usually ends in Bea hissing in defence, or growls when we pick Cass up to break it up. It's hard to end their play sessions on a good note, because it always spirals out of control.

I know it's early days but it's stressful as I feel I have to follow them around with a blanket constantly for any proper fight that breaks out. What should I do/will this pass/anyone have similar issues?

This is Cass

   

And Bea.

Your kittens are unevenly matched by age and stage. The three-month-old Bea is no match for the bigger, stronger 8-month-old Cass, and it also sounds like they have very different temperaments.

Cass is delighted to have a playmate and wants to use her kitten skills full-force on the fun little newcomer, who is nowhere near her skill level, and appears to have a much more docile nature to begin with.

You will either have to separate the two for good chunks of the day until Bea matures, or you will continue to supervise.

It sounds like Cass has not learned her social skills, which are generally taught by the mama cat. In her absence, you will have to teach her. When she begins to play rough, try hissing at her. She will automatically understand what this means. A firm "no" and a light tap on the head with your fore finger also works. She needs to learn how to interact gently with another cat, but it may not come easily as she has the size advantage right now.

Is she spayed yet? Spay surgery goes a long way to calming hormones as well!

Good luck and let us know how it goes. .

Thank you for the advice! I still keep them separate when we're at work or sleeping. Bea takes the study, but it kills me how sad she is in there at night not able to sleep in our bed with all of us.

How long do you think it will take Bea to mature into a proper playing companion for Cass? They really seem to like each other, I just want them to be happy.

Also Cass is desexed but Bea won't be desexed until two or three months in the future when she's an appropriate size.

Well, like I said, it's not all about Bea maturing. It's a great deal about you teaching Cass how to act appropriately with Bea. If you follow my tips above for disciplining Cass, it will go more quickly. I'd suggest you bring Bea into the bedroom too, and teach CASS how to deal with the newcomer. Does this make sense?