You can use a mix of John Innes No. 2 and good multi purpose compost, but you'll be somewhat restricted as to what you can grow by the depth of soil in the raised beds if they're sitting on a hard surface.

Sorry....Not sure if you mean type of soil etc or plants....It really depends on what you like to eat :-) Raised beds are perfect for root veg as the soil is not compacted and full of stones. Carrots are great and radishes provide a super quick crop! Runner beans provide masses of green beans (and if left to dry on the stems...seeds for the following year) Tomatoes, lettuce crops are all relatively easy to grow....and if you stagger the planting of the lettuce a few weeks apart your crop will last longer. Mint is nice too dangling down over the edge, nice for mint tea's (but tends to spread a lot so be warned!)
Nasturtiums add colour and the flowers and peppery leaves can be eaten....but snails love them too!
I have had great success with green peppers which grew very easily and profusely!

P.S. ( You probably have done this already but if not... before you plant dig loads of kitchen scraps into the soil, potato & veg peelings, banana skins, egg shells, even old newspapers and tea bags can go in.)

Good Luck! :-)

Sunrose, these raised beds are sitting on a patio, so depending on the depth of soil, runner beans, for instance, are unlikely to be an option, since they need a good deep muck filled trench.

What have you made your raised beds out of? How will water drain away if you have them placed on the patio? Just how deep are these 'raised beds'? It is more normal to create your raised bed on existing soil.

If they're open at the bottom, MG, they'll drain alright - all over the patio...

Thanks for all your help and advise, We have dug up the old patio stones and placed the beds on there, there will be plenty of drainage as it is mix of sand and rubble, then the beds ontop with a liner in. They are made of wood. We would have put them on soil but haven't got much room and the kids really want to grown some veg, so we are hoping this will work. I have read that you can have raised beds not on soil, is this right?

Will we be able to grow veg?

You'll certainly be able to grow lettuce and the like, but if you wanted, say, carrots or parsnips, then removing the liner at the bottom would be good - that way, anything which requires deeper roots will be able to get into the soil beneath, although it would be best if you could scrape out the aggregate/sand or whatever the patio was bedded on and turn the soil over a bit, incorporating some well rotted compost at the same time. If you just want the cut and come again salad style crops, they should be fine.

As Bamboo says if you only want to grow salad type veg. that should work, you could even grow carrots and pull them early to eat raw. It would still be useful to know how deep the raised bed is and what have you used to line the bed?

They are about 30cm high and we have lined them with weed control liner that the garden centre recommended.

Definitely not deep enough to grow root veggies well or peas and beans. Basically stick to salad crops and grow brassicas seedlings in trays to then plant out into the bed.

Copy and paste the link below into your browser

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

This is Garden Organics advice to school children on growing...

I would like to add that I am delighted you are creating the space for your children to grow food in, even if it isn't perfect! Feel free to send me a private message if you'd like more info