We have a dog, so we've not been on working stock farm sites. There are dozens of farm sites (I googled on "camp site farm" and many came up with their own websites), so I'm sure UKCS members will come up with lots of places for you. But do phone to check what you can actually get involved in doing (rather than just looking over the fence to pat the animals). And worth checking what the farmer has to comply with - http://www.hse.gov.uk/agriculture/topics/children.htm
If your quick you can do the night shift lambing tonight! We were busy last night so feeling very tired. I don't know if you can search on here for sites, don't think so. But if you read the feedback about sites some mention "helping out" so worth looking at farm sites and reading the reviews. Depends how much help your talking of.
------------- Visit Llandrindod Wells! Great scenery, walks, cycling, red kites. Ideal for exploring Mid Wales.
Insurance is an issue, you could never have anyone help at silaging / tractor driving etc. We have had campers at lambing time. They will feed the baby lambs, even sometimes lamb a ewe, depends on the campers....
------------- Visit Llandrindod Wells! Great scenery, walks, cycling, red kites. Ideal for exploring Mid Wales.
If you are ever down this way look up West Middlewick Farm Campsite - it's very rural (proper Devon!) but campers can feed the livestock, collect eggs, help herd the animals into the sheds and watch all the milking. Read the reviews - a popular site if you like countryside.