To think this shouldn't have happened

[Yellow98]

My Dnephew is 4 and is at nursery. He is non verbal autistic and has pica. For some reason, un noticed he managed to bite a lot of the plastic on the battery housing for a light up sensory type of toy. They were honest about it as he had swallowed a lot of the plastic. It contained a button battery. I don't know why he was left was this toy and how it went unnoticed that he managed to eat a lot of the plastic? Should this be reported?

Yes it should be reported. A child with PICA needs eyes on them all the time. There should be an EHCP in place for them to have the extra staff in place to manage this.

They will have self reported, as this is a serious safeguarding near miss.

You can ask to see their safeguarding policies (will be online anyway) and if you are not satisfied they have followed procedures you can raise it with OFSTED.