Hi! I really think you will just have to let it be. You have brought it up with the parents before and they brushed it off. Pushing it will only cause anger. Some parents seriously don't want to believe something and will stay in denial until concerns arise at school.

I have a 4 year old boy with many red flags for aspergers. I have brought my concerns to Mom ( obviously without any label, I'm not an expert) and she laughed it off saying they know and hope he'll outgrow those behaviors.

You should just carry on with what you are doing the best you can.