Interestingly, animated PNG (APNG) files seem to be so scarce that neither Gimp nor ImageMagick support this format. In fact, it took me quite a bit of searching until I found a way to scale an animated PNG preserving the animation (Gimp and ImageMagick can at least open respectively resize APNGs but only the first frame.).
For resizing an animated PNG I used the APNG assembler, disassembler, and ImageMagick. The workflow was as follows:
./apngdis animated.png for i in *png ; do convert $i -resize 32x32\< $i ; done ./apngasm output.png apngframe00.png 1 25 /f