Usually when they start eating solids. So, for the kids here, first 24hrs are the meconium, and from 1-3 weeks its the yellow milk poos which sometimes looked like clumped pellets, but they are still soft. 2 weeks and onwards once they are eating hay, grass, grain, whatever solids. They will become darker and then shortly after they will be normal pellets. Normal poo for 24-48 hours is the black tar poo(meconium) and from 2 days to whenever they start eating solids is a soft yellow poo. Not usually hard, but also not runny. Any off colors, runny poo, or excessive mucus and I will start looking into there might be an issue.
The yellow poop is sticky, make sure her behind does not get sealed closed if the doe isn't cleaning the kids rear end. Baby wet wipes do a good job of getting that gooey, sticky yellow baby poop cleaned off.
I agree with what everyone has said. Things that are not normal would be runny poo - diarrhea which could be a variety of things. We've had that happen a few times.
Too much colostrum can cause belly aches, and then there is ecoli. So any time a baby has a belly ache, or runny poop we give them a dose of Spectogard Scour Halt (labeled for pigs) and that tends to really clear things up quickly.
We had 6 does kid in the past week, and gave babies from 2 mom's some spectogard. They acted like they had belly aches - mom's had a LOT of milk and very rich colostrum. 1 dose and they were fine again.