I tried using clingfilm but it can be tricky to get it in place and it blows away easily. It stops the rain from deluging your seedlings but also causes condensation to build up in the sun which may cause mold: you will need to open it to leave breathing space.

Yes indoors it should work, so long as you remove the minute the seedlings start to show through.

Thanks for your prompt response. I'm going to try the cling film technique (indoors) with a class of 8 year olds tomorrow. Wish me luck.

Indeed good luck... The link below is to a useful veggie growing guide, primarily aimed at children but adults find it useful too!

http://www.gardenorganic.org.uk/growyourown/Vegetables-complete.pdf

I've used clingfilm instead of a sheet of glass in the greenhouse. worked really well too. enjoy the children.

I use pots from potato salad on small pots, they fit perfectly!

freezer bags are better than cling film....a little stick in the corners of the tray, bag over the top......perfect indoor greenhouse...