...http://www.musiciansfriend.com/navigation/avalon-preamps-compressors-eqs?N=100001+202034&src=3WWRWXGG&ZYXSEM=0
How old are your nieces? I could help more if I knew....and it may be a wise idea to talk with the parents first. I'm sure they can give you a lot of information to help you decide.
A vacuum cleaner. Chicks dig vacuum cleaners.