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

I decided to turn off the oil furnace plus I used a screwdriver to dislink the register cover

I started a daycare in the house last Spring, because I wanted to stay house with our youngest child. I didn’t want to put him in daycare plus having our own was the best option. I reached out to others in the community plus I ended up with 5 other children around the same age as our son. I had all of the children for six or several weeks plus then the weather started to turn colder. I had to turn on the oil furnace plus 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. Some of hours after I turned on the heat for the first time, I started to smell the most horrible smell. The smell was coming from the family room, close to the part where the kids play everyday. I was upset 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 plus 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 plus heavier as I got closer to the oil furnace air vent. I decided to turn off the oil furnace plus I used a screwdriver to dislink the register cover. The entire event was stuffed with food plus toys. I have no system which one of the kids was putting things inside of the oil furnace vent, although I dislinkd everything plus the smell slowly started to dissipate.

AC filter