is there something in particular to your area that makes it nicer for them to hang out there? shady tree? benches? if there is get rid of it.
also you said they were youngish? There is a range of sound that is audible to most kids and teens that most people above their mid 20s are unable to hear, and its really high pitched and annoying. heres a link, might be worth trying out.
http://www.compoundsecurity.co.uk/te..._products.html