Is it strange for people with williams syndrome to have a fascination with children's cartoons? as a grown adult, or teenager.

Probably no: Williams syndrome is a disorder where the personality is called cock-tail personality. Very outgoing personality without inhibitions. Although they are outgoing they do have developmental delays and can have low normal IQ. I do not believe it is strange to have a fascination with children's cartoons. Would be based on this person's IQ.