Co-Living

There are several things that may lead to this. Some less savory than others.

1. Extended family

2. Short term economic hardships

3. Undocumented families

4. Govt. subsidized "emergency housing"

Similar to Social Services putting an entire family up in a single motel room for months on end.

5. Short term rentals

It does happen but this does not sound like the situation you are describing

6. Cultural

This type of multi-family communal living is more common in some cultures.

7. Remote possibility that they are being used as stash houses

These are where smugglers will house people temporarily while they either pay or work off their debt. More prevalent in some areas but truly not the norm. Also, less likely when there are multiple children involved.

8. There are lots of little things that law enforcement look for when trying to ascertain what types of activity may be taking place. Or maybe nothing nefarious at all.

9. If the economic contraction continues, this type of unconventional living arrangements may become more and more common.

10. To answer your question, There are some communities in the U.S. where this is quite common. And others where up until now it was very rare. The times they are a changin.

Eyegor