Chiisana Viking Vickie

Both are children's anime and fun to watch. Both are co-production with another country. By coincidence, both have 78 episodes. Moomin is fantasy, while Chiisana Viking Vickie is not. Chiisana Viking Vickie is more cartoonish. 

Although they are different, they both tell the story of pirates and vikings going on adventures. Eichiro Oda, who created One Piece, has stated that Vickie The Viking is his biggest influence and the reason why he created the One Piece manga to begin with. 

Episodical show for kids about a kid and his friends and family in a historical period and their somewhat mischevious adventures. 

Both these anime are from the seventies and partially from the same producers. Both go about a little boy who is having some adventures on his own. Both in their own (historical) environment.