What to do about suspected drug deals next door

The title is pretty self explanatory.

In the last few weeks, my next door neighbor has become rather popular, but only for 5-10 minutes at a time, when the visitors subsequently leave.

I have no real proof that it is drug dealing, but i'm at a loss to explain why lots of people (some 'regulars', some i've not seen before) keep turning up at the door.

The trouble is that the person in question is a woman (middle aged) who has a small child (6/7 years old) so i'm loath just let the police know.

There's also a two guys who come round (as a pair) way too often, since they've been arriving we've had loud music all night, have been banging on the door at 6 in the morning and staying over a day or two at a time.

It's since we first saw them that the visitors have been arriving, so I have thought that maybe they're dealing through her (in a coercive way)

Any thoughts?