My sister had 3 kids when she finally went for help, it took over a year of rehab, continued support, drug testing and most important "A willingness to stay clean" before she got her kids back. 2 of her kids she had she remained clean all during the pregnancies, after her 3rd she left the hospital to go get high. I never understood that. Today she is 5 years clean/sober and is probably in a better place than she was long before the drugs, she homeschool's the 3 oldest kids and also has a 4th now. (2 years old)
So recovery is possible and it is very possible that your daughter will one day be the mother those kids need. Prayers and hugs!