If the baby is eating pellets and hay it should be fine without the milk. If mom is attacking the baby I would separate them.

If you wanted to give it a supplement, I’ve heard that kitten milk replacement (found at most pet stores) is the best thing to use. But if he’s eating pellets and hay, I think he’ll be fine without mom. I’ve read that most rabbits are weaned by 6 weeks anyway, the extra time with mom is mostly to help boost the immune system and let the gut settle, not because they still need milk.

If the bunny is eating enough and maintaining weight- I would weigh on a scale meant for small stuff (kitchen scale, postal scale, etc) daily- then I would not supplement with milk.  Fresh goats milk is what is one of the things recommended for baby bunnies- and Mom only usually feeds them twice a day or so- so they need a milk that is high in fat, etc. I used to rehab baby cottontails that were orphaned and it is a brutal task and heartbreaking.  Their systems are so delicate and there is such a fine balance.  There is a milk replacer made just for baby rabbits- made by Fox Valley but you would most likely need to special order it.

Baby bunny guts so so delicate I would honestly NOT give it milk replacer or goats milk unless you have to.  Weigh it daily- best would be the same time every am before offering greens, more pellets, etc.  I don’t think it would drink it from a bowl so you would have to bottle feed or syringe feed it.  I would maybe try a pellet slurry before goats milk.