The idea was really amusing, but the concept wasn´t carried out very well. The script writers of this prequel about Jönssonligan as kids, didn´t bother to watch ALL the existing movies about Jönssonligan as grown ups, so this movie isn´t very consistent with the frame story as it had hitherto developed in the duration of the seven movies about the gang as adults.
Hence; The gang originally consisting of Sickan, Vanheden and Rocky, Vanheden´s first cousin Dynamt-Harry showing up later as a fourth member of the gang, Rocky then disappearing (as actor Nils Brandt had passed away) and Harry meeting Doris at that point.
Now, we are suddenly to believe that all of them - except the completely forgotten-about Rocky (sic) - were class mates at the age of nine in 1954.
Furthermore, in the very first movie Varning för Jönssonligen we hear from dialog between Vanheden and Wall-Enberg, that Wall-Enberg was born in 1923, and married at Seglora kyrka on June 6, 1945. In the same movie Wall-Enberg hired "Biffen", who was a harbour worker, to eliminate Sickan, and it wasn´t until the third movie "Biffen" had become Wall-Enbergs chauffeur.
Now, all of a sudden, Wall-Enberg and "Biffen" were ALSO class mates with the gang in 1954. Sequel/prequel consistency ZIP!!!!
Despite all those flaws the movie is really amusing, but it actually doesn´t work as a prequel to all those movies it bears no consistency with. That part of the concept could have been much much better done.
Where is Vanheden´s brother Leopold? (Also mentioned in Varning för Jönssonligen).