Seeing these two groups on tour is like witnessing a kiddie-pop changing of the guard. IMx, once known as Immature, is the last of the early-’90s R&B boy bands (remember Another Bad Creation, the Boys or Hi-Five — do ya?). These three randy lads spent the ’90s getting their man-hairs in front of loud teenage girls all over this land, evolving from prepubescent playas to, well, drinking-age playas. Now that IMx is grown up enough to get explicit without sounding inexperienced, this new boy-toy quartet known as B2K — already a fixture with the TRL crowd — is here to pick up the PG-rated, screaming-nymphet slack. So while these new kids are on stage making the 16-year-old girls all warm and mushy inside, IMx will be right behind them, trying to sex up their mommas.