I am looking for sauce on an old, old animu, an OVA or film from

File: mystery_animu.jpg (193KB, 901x1022px) Image search: [Google]

193KB, 901x1022px

I am looking for sauce on an old, old animu, an OVA or film from probably the 70s or 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 fantasy-scifi and probably for children.

Does it ring a bell for somebody? I have looked everywhere and literally nothing came up. Help me /wsr/, you are my last hope.