That's a normal problem. That's why young robos are so  very difficult to sex. There was once when I sexed them wrongly and end up inbreed. But only once lar. The babies were not used for breeding. Just seperate them from the rest and be good to them till they passed away.

The obvious difference is really just the distance between the anus and also that male testicles become obvious overtime.

If you wish to tame them then don grab them.  Let them come to you. Patience, my friend. Everything will go fine.