Anyone with experience of those mini gardens in a compost tray things?

[Hangingbellyofbabylon]

It's our allotment show at the weekend and the girls want to enter the 'mini garden in a tray' category. Was thinking along the lines of a bit of moss, maybe some grass and a little mirror to look like a pond? Have no real idea on these things - has anyone done well in these and has great ideas? must be fairly foolproof as dd's are 3 and nearly 5. thanks

[Hangingbellyofbabylon]

bump - this is so mumsnet - someone out there must have made one of these