The mother hen (even if she is just a surrogate mum but doesn’t know or care) teaches them to peck.  She pecks and then they copy her.  The chicks eat chick crumbs whilst the mother has her own food which is not suitable for the little ones.  The last egg has not hatched although, when I picked it up, it was still warm.  I will take it out of the nesting house later as the hen is concentrating on teaching the chickies how to peck, eat and drink.  They still need to spend time under mother hen to keep warm and will do so for some time to come.