Try if they will like these:
Porwanie Baltazara Gąbki
...
Miś Uszatek
youtu.be/Bo4dYjb5Rro
Chojrak, it's spookiness is too confusing.
I like it ;) but you are right if the children are small, it might be too scary for them, so don't show it.
You want 100% Polish cartoons, and not only with Polish dubbing like Muminki etc.