I think this show is very educational and is useful in teaching young children about the life of the young Amadeus Mozart. It teaches about different elements of music, such as tempo, different instruments, and the like. (Also: there is a segment done after the episode, called "Monti's World, which provides additional information.)
What parents should know:
Positive messages: It promotes music knowledge and appreciation. Amadeus pulls pranks, but they are innocent.
Violence: There are pratfalls, but no one is hurt and is played for comedy. However, in one episode (Season 1 Episode 4: "Kidnappers"), Devilius plots to kidnap Amadeus to learn his secret to success. He hires two criminals to capture him. One asks what will happen if they don't kidnap him, and Devilius replies with "Then, you can say your last prayer!" This may go right over children's heads, but is still disturbing. In the same episode, Amadeus and Kajetan almost drown, but are saved. In another episode (Season 1 Episode 13: "Never Kiss An Empress"), Devilius beats up a guard to steal a disguise. This, fortunately, is offscreen. In another episode (Season 1 Episode 1: "Solo For Amadeus"), Devilius scolds Mario and violently shakes him. Throughout the series, he threatens to send him back to Milan.
Sex/Romance: There is no sex (this is a children's show, after all!), however, there is kissing. Amadeus and Mario are in love with the baker's daughter Kati throughout the series. Amadeus kissed her (Season 1 Episode 3: "Pumperl In Trouble") and so did Mario (Season 1 Episode 2: "The Stolen Watch").
Swearing: Uses of "heck" and "lame", but these are not swears. However, in one episode (Season 1 Episode 11: "The Dancing Harbor"), Monti says "Wow! Hell's broken loose! I can't believe it!". This, fortunately, is the only use of the word in the series.
Drinking/Drugs/Smoking: No drugs or smoking of any kind, however in one episode (Season 1 Episode 13: "Never Kiss An Empress"), Devilius and Mario have dinner, which is served with a full glass of an unknown drink (possibly red wine). Devilius is about to make a toast, but is then interrupted. Not a single sip is taken. However, this may not count as drinking because the characters are Italian, and it is customary for Italian children to have wine now and then.
Misc. content: In one episode (Season 2 Episode 4: "Smallpox"), Nannerl faints at a concert, and people worry she will die. She doesn't, but this may be scary for some children.
Conclusion: Overall, this is a great show for children, and I highly recommend it.