IME most lambs don't like most creep feeds for a long time, and most calves don't like most calf feeds ever

However, lambs seem to
love Champion Tup Mix, so that's what pet lambs get here. They start playing with it in their third week and eat it properly by 3 weeks old.
Lambs out in the field with their mums will copy mum eating whatever you give her. As soon as we have a reasonable number of lambs mouthing on at the ewe nuts we switch to Davidsons' Pearl Lamb Non-GM Lamb nuts, and any sheep that are being fed get that all summer.
For all that the lambs in the field seem to like the Pearl Lamb Nuts, they don't seem to be as appealing to the pet lambs at first; I think in the absence of a mum to copy, the variety of shape, size, taste and texture in a mix is more likely to tempt a baby pallette.
(Oh, and it's taken me some time, but I have now found an equally appealing calf starter feed. Would you believe it's Champion Calf Starter.)