ALVINNN has evidently aged the characters up as high schoolers (could be to share some sort of continuity with the CGI movies since they were in high school), but at times, you wouldn't be able to tell since they still engage in certain kinds of activities and passtimes normally associated with younger kids (like when they were eight in the 80s cartoon), such as Theodore playing with stuffed animals (in this case, his Talking Teddy doll), or Alvin playing cowboy (but then again, we know even Bert likes to play cowboy at times). Sadly, in Theodore's case, he seems to be suffering from Flanderization: he's increasingly become the naive little baby of the family, and that seems to be his defining characteristic now.