No comma required.
Don’t put a comma between the two verbs or verb phrases in a compound predicate.
Incorrect:We laid out our music and snacks, and began to study.
Incorrect:I turned the corner, and ran smack into a patrol car.
http://owl.english.purdue.edu/owl/resource/607/02/
Yep, your right. ;-)
There are two subjects in that sentence. A comma is required when there are two subjects.
"We are all adults and should know this!" needs no comma.
"We are all adults, and we should know this!" requires a comma.