I know we can probably laugh about it, and marijuana is now legalised in many parts of the USA anyway under various conditions, but yes, there are also a range of very bad outcomes here. I personally don't have sufficient confidence that this could never be pinged on to the OP, in which case the results could be devastating.

The basic problem here is that the villa was not cleaned with sufficient vigour between bookings, and the BA dimension here is that they have a property on their hands where the housekeeping was not to standard, it wasn't just the weed. Now it may have been a one-off - the villa company had some appalling guests beforehand, who perhaps checked out very late and giving only a short window before the OP and family arrived. And they rushed the housekeeping as a result. Even appalling guests tend to want to retain their stash (I suppose) so that scenario - if a one-off - is what it is. But let's say there are a pattern of complaints against this resort - in which case BA had better take them off the list until the management sort themselves out.

So I agree with KeaneJohn that you should call / Skype BA Holidays (not BA's contact centre) at your earliest convenient opportunity and discuss this on the lines of "does this villa company have a bad track record?". Personally I think this is the sort of thing which after the event is very difficult to remedy - having police tramping around your holiday isn't very relaxing to say the least and the damage is done. But feel free to suggest remedies to BA Holidays. At the lowest end you could perhaps suggest you take your family to a morale boosting supper with BA taking the tab, but with BA then billing it on to the villa owner.