I definitely think the transition was jarring. Hopefully they'll do a flashback or something to explain whatever happened to the original kids. One of the upcoming episodes sounds like it'll try and fill in some of the gaps:
Hopefully there is some sort of explanation.Young Justice: Invasion
Saturday, May 19th, 2012 at 10:30am (ET/ PT) - "#30 Salvage"
While Superboy and Blue Beetle battle Intergang, Nightwing and company try to salvage the soul of a former comrade fallen from grace.