Last year, my children were just interested in what would come out of the ground after they had planted their seed.
However, there were times when I spent a lot of time digging my plot and the kids had little to do. Therefore, I just gave them their own little area to do what they wanted with it. Yes, they dug holes!!!
I have three children, so knowing the rules of the allotment, they wandered off and did a bit of hide and seek, played with someone's dog and dug more holes (on my plot). The also loved the rides in the wheelbarrow.
This year, I will arrange a treasure hunt on my plot. I intend to draw a map including clues and directions etc so they can find the pre-planted treasure.
I'm also planning to buy some child size tools so that they can maintain their own little bit of the plot. Who knows, they may even eat their veg and fruit as well.
Another game we play is spot and name the vegetable and/or fruit. Kids these days know very little about fruit and veg only that its available in packets from your local Supermarket. Shame!
My kid's school also run a Garden Club. My daughter is too young to attend (she is year 1) which is a shame because out of my lot she is the most knowledgeable and interested.
I too would welcome further ideas from parents who keep their young ones busy, amused etc on the veg plot.