Hi and congrats on your two new bunnies!
Can you give us a bit more info about what their diet is like? A bunny’s diet should be 85% high quality hay, 5% pellets and 10% leafy greens, introduced slowly from this sort of age.
Healthy bunnies produce two types of poop. The dry round pellets, and glossy darker squishy poops that look kind of like a bunch of grapes, called cecatropes. They’re meant to eat these cecatropes straight away, but sometimes they produce too many and leave them lying around. Often they produce too many if their diet is too rich, for example getting too many pellets. Is he producing regular poop as well as the dark damp type?
I know you didn’t ask, but the other important thing I’d like to mention is that the boy and girl should be separated. At 3 months old, the girl could get pregnant, and pregnancies at a young age can be very dangerous for mum and babies, not to mention a lot more bunnies than you planned for. When both the buns are around 5/6 months old you’ll be able to get them neutered and go through a bonding process to put them back together. While they’re separated, you can keep them in sight of each other for comfort, but make sure there is a 6 inch or so gap between the bars, as bunnies can mate through bars! You can also spend this time swapping them between areas so that they remember each others scent and don’t get territorial, making for an easier bond later.