What songs are good to sing for my son's talent show?

My son is a 4th grader who entered the talent show. He started out singing "We're the Champions", but the instructor was worried the teens hat will be in the audience will make faces and not like it. What are some good songs? The instructor likes to hear my son play piano, so he would like it if my son could sing and play piano. My son is lv.3 of Alfred's Basic Piano Library. He is Lv.4 on Theory by Julie McIntosh Johnson.