I don't know if there is a solution. Doing the above isn't fair on the children, but might stop the parents (and others who see the risks). Doing nothing means they will just carry on. What's needed, is a way of punishing the parents without causing problems for the children.
Maybe simply requiring the long term unemployed to work in teams cleaning up the local area - picking litter, removing graffiti, etc. If childcare is a problem then at least for couples, they can work in shifts. Single parents where the other parent is known can do the same. Single parents where the other parent is not known, findable or is a danger could be checked and teamed up with other single parents.
It's probably unworkable for many reasons, but at least worth considering.
SteveW