Can you post a picture? Save to your computer then post. What shape are the slabs? How thick? what kind of wood? Are they end grain ,or long grain? It helps if we know all the details.
I usually use an 1/8" or 1/4" quarter round bit if i want a simple edge.
It is hard to get a full round with this bit, but can be done on a router table with the proper fence set-up. I use half round bits on the router table to get a full half round. But if you don't have a router table then go to the 5/16" quarter round and you will get very near a full half round routing from both sides.
The problem is that with the bearing guide, the first cut will be 1/2 of the way down,on a full 1/4 round bit and the bearing will drop below center of the edge and will then not give a true half round overall.
The slabs are 2in and 4in. Cypress Pine. I'm not sure what size of roundover bit to use, I just need the edges slightly rounded. The cookies are end grain 2-3 1/2 in dia and the long slabs are 3 yards by 2-3 feet.
I will be doing it handheld with a Dewalt 625.