Kids don't have the same standards as we, the Great and Powerful Masters of All, not to speak of Being More an Better, Etc. Thank God. Any plants that have relatively tall-ish stems from a rosette that can be stripped of lower/shorter leaves, -woody or not, and can be made into something that is a more or less tropical/jungle looking palms, including palm seedlings, and figs are good candidates, too, especially Ficus benjamina, "Too Little", of which there are many varieties. Bulbletes or other tiny offsets of corms or bulbs can work well. Lilies, Calla Lily, Caladium, often have ~immature bulblets attached that we ignore, but can be removed an grown-on as a tiny plant.
You can utilize bonsai techiques by restricting the roots of your terrarium occupants by keeping them in containers. Pull them out when they get too big and trim the roots and put them back in. The little cups for coffee makers are useful. The platic tops from lots of consumer items from spray paint cans to large containers of washing machine soap can be used as pots. You can drill drainage holes in them, but cleaner holes can be made by heating a nail held with a vice-gripes red-hot with a Burnzomatic torch. Poke drainage holes in the sides rather than the bottoms. Paint them flat black for camoflage. This will make it easier to replace non-preforming items, muy pronto. If you use sunlight, you will grow algae and everything will lean towards the one side.
If you find a good source for fairies, let us know! (We have plenty of Trolls here)