What is the neck size for this tie?
14.5" to 20", this band is adjustable.
What are the measurements of the pocket square?
9” x 9” .
I have a 10 year old will this work for him?
I think it's possible, but it depends on the size. Also you can check this Pre-tied Boys Bow tie ASIN: B0B9X1GQMW, it's for boys and in same pattern.
Is this bow tie pre-tied or untied?
It’s untied. But I followed the video on the product page to do it and learned it easily.