It took until they were almost 1 year old for some of my young rats to stop having baby poops. As long as it's not straight up liquid, it might just be an upset tummy or baby poops.
If you want, try cutting all treats out for a while, and slowly introducing them back to see if that affects the poops.
You can also buy dog/cat probiotic on Amazon to give them. This is the one a rescuer recommended and it seemed to help.
I get this liquid form from amazon - beep. It seems to help. And it's easy to hide in chocolate sauce or something.