Uninvited Sims won't leave.

I'm experiencing this with Businesses and Hobbies. A bunch of sims who aren't customers will show up on the sidewalk in front of my lot, and they'll just stand there all day. Some of them will come onto the lot. Some of them go into the residential part of my building even though all the doors are locked. There's no send home button when I click on them. I have to use the TOOL mod to get them out. I've also seen a few toddlers wandering around by themselves. Not sure if that's related. 

Has anyone else had this problem, and do you know how to fix it?