Carrot varieties?

Slugs and snails are rather fond of young carrot leaves (and the small black keel slugs of the roots too!)

They can be even more of a problem if you net securely against carrot fly and hence let them get on with their evil deeds "under cover" - chucking some slug pellets underneath is a good idea, especially as you won't risk affecting other wildlife.

Before I stopped leaving it to chance and invested in netting the tell-tale sign of carrot fly attack was always the leaves starting to turn red. 

Yes it will be slugs ive been there and done that with the seedlings they demolished them overnight,i have to put slug pellets down.
As long as you keep the soil moist once youve sown the seed till they come through,then protect against slugs and carrot fly,a piece of mesh is about £20 and one of the best investments ever for the garden,a few hoops to hold it up as well.
Then give them a decent thinning out,i just lift the edge of the mesh and work along,no need to take it completely off,a few weedings as well from time to time,providing youve got a half decent soil they should be ok.

try eskimo comes high recommended in scotland they leave it in the ground and dig them as they need them in the winter but just cover them with fleece for frost