Yes, our goats will eat elder but not the sheep. As with in the hills, I had a ewe die a couple of years back to rhodie poisoning. It makes you very aware of what's in your ground and it does only take a nibble.
If you have anything with shiny leaves - azaleas, laurel etc then they will poison, yew, privet as already mentioned and I'd be wary of any other evergreen plant. These are all the usual culprits, but things like deadly nightshade etc, things that aren't common could catch you out. Laburnum trees are highly toxic (that's the ones like big yellow chandeliers) and surprisingly there is a farm near us with several on the grass verge, also another smallholding nearby with laurel within stretching reach
If I had an animal plant poisoned again I'd have it shot quickly, it's a horrible death for them and even if they do manage to survive they can have problems later.
Good that you're sounding out before any problems. Your lambs sound grand though sophie and obviously like their own bedroom
quite right lambies