I know a lot of you may have done this already with your kids, but I thought it was worth a blog anyway! I think the experience of growing cress and then making sandwiches was the first time my son Freddy worked out that some food grows and then becomes lunch. We bought a nice little cress growing kit (that kids can decorate) from Homebase for £2.99:
We planted the seeds together, put the kit on the windowsill and watched the cress grow over a few days as we watered it. He then helped me chop up the cress (child scissors may be best for this), add it to some egg mayonnaise, and make sandwiches. Freddy was quite proud of himself and still remembers it! I took photos of the whole thing so we could talk about it afterwards.
The end result!