Basically anything that you can then play with, keeping in mind that if there are more steps then their age they might get bored.

Boxes with lids
Drinking fish
Fortune teller
Boats
Things that spin
Architectural origami (origami lego) is also great fun.

https://www.origami-fun.com/origami-for-kids.html

My spinable lazy susan
Https://steemit.com/original-design/@gmatthe2/how-to-fold-a-spinable-lazy-susan

https://web-japan.org/kidsweb/virtual/origami2/exploring01_09.html