The baby could be with his mother in prison - Styal in Cheshire has a good mother and baby unit. Pregnant women given birth at the local hospital and return to prison with their babies.
There is also a mother and baby unit at the local hospital, Wythenshawe where mothers with serious psychiatric difficulties can stay with their babies. I'm more familiar with its use for women with post puerperal psychosis than mother's who stabbed their partners but I'm sure if it was the right place, they'd take Helen.
merlotgran - nope no way would the police only try to extract information they can use in their favour if they're determined to find someone guilty. They'd be slaughtered (metaphorically) by the Judge if they did that. The whole emphasis of police/sw training is to enable them to help the child tell its story, without leading the child in any way. Best Evidence Interviews aren't perfect but they are the best we have, currently.