I'm the family cruise editor here. Actually the Navigator's youth facilities are very different (and even larger) than the Explorer's. If you have teens, definitely pick the Navigator. It has a number of teens only areas including outdoor grill, teen area for sunning, etc. that no other ship has. If you have younger children, they'll love either -- we cruised on Explorer in June and my 8 year old LOVED the youth program and ship. I wrote on article on this section of CruiseMates.com on our experience aboard the EOS.
Let me know what you choose.
Smooth sailing,
Luisa Frey Gaynor