A-Next was a new generation of Avengers, yes. I think a big difference though was they weren't kids, they were adults (well, J2 was a kid in an adult's body and Spider-Girl was a teenager, the rest were adults). Plus their costumes didn't look, y'know, bad.

Almost every superhero has seen some future history with their kids carrying on their legacy, in comics. Doing an animated movie about the Avengers kids (and based on the trailer I saw it's not based on the Ultimate movies, it's classic Avengers) when there hasn't actually been a movie about the Avengers seems kinda stupid to me. The uninitiated will look at this and go "Who?" You get more leeway in the comics.

~Hat~