Hi George 12, A home with 4 children under 4 is going to be a bit chaotic ie wear and tear, scattered toys, clothes, bedlam etc unless there is a strict regime in force.
You say the wife in this situation is a nurse and is never there and that the husband is is stay at home dad ? Now, having 4 children in as many years, must mean that this lady must have been home for maternity leave etc so it is odd that she 'never seems to be there ' ?
Are you sure the children are being locked out, or are they being sent outside to play ? Are they distressed, crying, neglected ? Do you know ? Perhaps the dad is watching from inside ? I'm saying this before jumping to conclusions. Neighbors can have personal reactions to others behaviors coming from subjective viewpoints. I have had experience of this in my neighborhood .
I am aware of a privately rented house which is ,from the outside , unkempt, tatty, embarrassing to the the locality, but the family functions extremely well. (Landlord is the one who does not care by the way, in contrast to yourself).
So I would take a careful path on this, but if you think your neighbour's fears are justified ,of course you have a responsibility to contact social services. It is a huge undertaking and responsibility.