There's something in the closet

Since years ago I bought this 3 story house for my family. The previous owner suggested that we shouldn't open the children's bedroom closet.
Of course I thought he said that to gain the interest of paranormal enthusiasts but we weren't, but we promised never to open it.
We moved all of our stuff. The youngest of the family thought he heard a rattle of the closet in front of his bed so he covered himself with his bedsheets for the rest of the night.
When he told us we thought he was having a nightmare or that he imagined this whole situation. We told him that everything was ok.