Hi M.,
I wouldn't be so concerned about the cultural differences as much I'd be concerned at the AGE difference. Teens in any part of the world are "know it alls" and can be rude and mean to small children.
My sister hosted a boy (I think he was 14 or 15) from Spain. He was such a polite cute little boy, she had no problems.
She had a 4 y/r boy then and a 2 y/o girl.
She noticed her son started acting very "baby" like and being very sensitive and whining.
She then became very wathcful and heard the boy saying things like "You're a baby" "leave me alone baby" and definately introduced him to some questionable music, skate boarding things etc.
Not bad, just a little early for the boy and the name calling, although "not bad" was hurtful to her son and his self esteem hurt over it.
Teens get annoyed by kids easily.
I would wait until your kids are older, right now the won't know the difference in culture anyway, the teen may teach them some new words in another language but it's a gamble bringing a teen in with small kids IMO ;)