No they are not. Only those chidren under one year, which will not include this mother's other child.
That according to the link provided by the808brass, which says in part:
The couple also have a 16-month-old son, who is being held at The Children's Shelter in Austin.
Crimmins said Jeffs and her infant will be placed in a shelter together, assuring their safety. CPS has allowed mothers to remain with infants 12 months old or younger who are in state custody.
The older son wasn’t with her because she was in the hospital.
The “mothers staying with children 12 months and under” are adult women.
Minor girls with children are being placed together.
http://www.foxnews.com/story/0,2933,353919,00.html
You’re confusing minor mothers and adult mothers. Adult mothers were only allowed to stay with their children if the the children were under one year old. Minor mothers are being kept with their own children of all ages, to the extent the state has been able to figure out which children belong to which mothers. The Children’s Shelter may be where both this minor mother and her first child have been staying, or it may be a temporary shelter equipped to handle very young children without their mothers, where the child was placed while his mother was in the hospital giving birth.