At the end of the day it's not a film for introducing one's kids to Astérix - buy the comic books for that. It's more a capture of the flavour of the Astérix books for those of us adults who remember them with affection, and who consequently aren't concerned overly with details of plot or characterisation. In fact Astérix and Obélix are woefully under-characterised from the start of the film. If you don't know that Obélix's trade is in quarrying menhirs, then the joke about the heart-shaped menhir for Panacea (Laetitia Casta) is likely to fall flat. But those of us who know and love the characters already are going to enjoy it.
One reason for not showing it to your kids would be that there is the occasional crudity in the language - in my view utterly unnecessary, and against the practice of the comic books - at least the English translations of same.
One of the joys of the English translations of the books was the pains taken by the translators to include jokes specifically for the English, particularly in character's names, eg the chief is called VitalStatistix, the druid is called GetAFix, Caius Bonus becomes Crismus Bonus, etc. Terry Jones has happily continued this tradition, although it's a shame that he didn't do more, as it seems to me that movie script rather emphasised silly japes and slapstick over the wonderful wit of the comic books.
Dèpardieu is an absolute revelation as Obélix (and in the English version, splendidly dubbed by Terry Jones himself).