I have used the 70-300VR for daylight youth football on a full-size field. It works perfectly. Before that, I used the earlier non-AFS ED version. It was good too, but the newer lens is sharper and focuses faster. 300mm on DX is probably all you need for youth soccer.
Now, on a 60-90 baseball field, I find that 300mm is too short. Well, maybe not too short, but the 70-300 VR doesn't stand up to big crops at 300mm wide open. I have often considered getting the AFS 300 f4, and maybe adding a 1.4TC for shooting outfielders (my son plays CF, so this is a biggie to me). I figure the 300 f4 will be sharper and allow for better cropping. The extra stop is great too.
I don't shoot youth soccer, but I see it going on all the time. I have never seen a game that I could not have shot with the 70-300VR. Now, if you have to shoot at night, this lens is useless. As others have said, you need an f2.8 lens for that.