I'm inclined to think that parenting classes should be compulsory for everyone. I don't think just targeting families or children who are seen as a "problem" is a good idea because it stigmatises and creates a negative vibe to start with.
Personally speaking, I wish such a class had been available when I had my first baby because I hadn't a clue. Some information about play, how to de-fuse difficult situations, etc., would have been very valuable to me.
As others have said, having made huge cuts to council budgets which has had a knock-on effect for provision of child care services, and having dismantled a large number of the Sure Start centres, it seems a bit rich now to try and demonstrate a commitment to helping families. Also, the most clued up families can only do so much to aid their children's emotional, physical and intellectual development if they are working all hours and living on the breadline.