This specific episode begins with the Romans sending a spy in to the village to discover their secret source of strength. Very soon, the Romans kidnap Getafix in the hopes that they could cajole the potion's formula out of him. However, the Romans are lined up to pay dearly because nobody lays one over on the Gauls without receiving a serious pounding on the skull!
Most Asterix titles are aimed at a teen/adult audience and they cleverly integrate many historical events in to their plots. There is also a deeper satirical presence throughout these books, and for that reason I feel that children under the age of 12 or so would not quite appreciate the humor. The violence is more along the lines of black eyes, dented armor and missing teeth, and hence should not worry a parent too much. This is one of the best Asterix comics, and since it started the chain reaction, this is the one to get FIRST!