I am looking for suace on an old, old animu, an OVA or film from probably the 80s. I don't know the author, and the translated name was roughly "The children's kingdom", though the original name may be completely different.
The memories of it are spotty. There was a space battleship yamato-like ship in there, pic somewhat related. There was also a space train a la 999 in a scene where a robot with a cup as a hat autodestructed.
The protagonists were a group of children that travelled somehow from the earth to a space kingdom where they were attacked by the bad guys and had to go rescue the princess at a space castle (because why not), using the ship. The plot was definitely fantastic-scifi and probably for children.
Does it ring a bell for somebody? I have looked everywhere and literally nothing came up. Help me /a/, you are my last hope.