School Poly tunnel - advice please!

Hi All, I've just started as a school secretary. Last spring the school built a poly tunnel, but its never been used!
I've been told I can have half on the poly tunnel for my own use, if I grow plants in the other half with the children. There's also a veg and flower garden.
I have 2 issues, the first is money and the second is getting stuff growing which the children can eat at snack time, bearing in mind that the children break up for the summer hols early July.

I'm thinking of growing cucumbers, cherry tomatoes, peppers and maybe having a go at melons any suggestion of anything else?
I was also going to grow outside sun flowers, pumpkins, potatoes, raspberries and strawberries and sweet peas.

Am I too early to start sowing now to try and get a head start. I have a heated propagator that I can use in my greenhouse at home to start seeds.

Radishes, Peas, Lettuces? (I know children don't in general like lettuce but they'll be available)

I realise this isn't your problem but why did the school waste their money buying a polytunnel if they didn't have a keen gardener to use it?