I don't know who started putting stuff in the furnace register

I started a daycare in the house last spring, because I wanted to stay home with my youngest child. I didn’t want to put him in daycare and having my own was the best option. I reached out to others in the community and I ended up with five other children around the same age as my son. I had all of the children for six or seven months and then the weather started to turn colder. I had to turn on the furnace and that meant using the registers on the floor. I talked with the children about safety with the heating registers, even though they are made to be cool to the touch. A couple of hours after I turned on the heat for the first time, I started to smell the most horrible odor. The odor was coming from the living room, close to the area where the kids play everyday. I was worried one of the toys might be on fire. Sometimes accidents can happen with toys that have batteries for electronic sounds. I went through all of the toys and I didn’t find anything that seemed to be the source of the smell. As I was looking through the toys, I noticed that the smell started to get heavier and heavier as I got closer to the furnace air vent. I decided to turn off the furnace and I used a screwdriver to remove the register cover. The entire event was stuffed with food and toys. I have no idea which one of the kids was putting things inside of the furnace vent, but I removed everything and the smell slowly started to dissipate.