If one of your rats has already killed a baby in the past, I'd probably wait till your little ones are at least 3 months old, so they are bigger and can hold their own.
If the rats are in similar size, you could try but be very very cautious. The Bindi might be the same size as the babies, but she is faster and more experienced and knows how to dominant. I know if they were my rats, I would wait especially since Bindi has already killed before. It's better safe than sorry right?