Closing out a pretty great year for children's movies — Up, Cloudy With a Chance of Meatballs, Coraline among them — Betty Thomas' dutiful animated and live-action sequel to 2007's Alvin and the Chipmunks brings up the rear with capable mediocrity. It's not entirely Thomas' fault: What are you going to do with those fat-cheeked, helium-voiced singing critters but slap together enough "awwww" moments to make the toddlers happy and enough knowing winks to keep parental bums in the seats? Except that these days, even the under-10 market has to be carved up, sectioned off by gender and genre. Enter the Chipettes, a rootin'-tootin' sassy girl group voiced by Amy Poehler, Anna Faris, and Christina Applegate, to compete with, then cozy up to, rambunctious Alvin and his pals (same guys as last time). With Jason Lee's Dave in the hospital and more or less out of the picture, our furry lads run amok at school while under the benignly neglectful care of a shy dweeb (Zachary Levi) with a feeble subplot of his own to trudge through. The rest is a horribly loud, partially comprehensible, and half-assed action movie, strewn with homilies about staying true to your sisters and bros, which just about every studio except Pixar lazily serves up below the PG-13 cutoff.