Thank you all for your advice.
May I please say that neither I nor the rest of the family would dream of accusing all Health Visitors of this kind of attitude. Most are indeed well-qualified professionals, but this family has been unfortunate.
There is nothing odd about the HV still calling - this is normal here in Denmark.
What this particular woman is basing her assessment on none of us know at the moment. I have suggested to my DD that her husband, being the Danish person in the household should ask her what the assessment is based on, and if necessary write a formal complaint to the HV's supervisor.
I assume that the guidelines for assessing children in immigrant households where the parents have a poor or practically non-existent command of Danish are being brought into play here, although they are not applicable.
I myself have tried unsuccessfully for years to get the teaching profession in Denmark to realise and act upon the fact that Danish language tuition for immigrants is nowhere near good enough.
The child's hearing and motor skills are normal, but the crèche he has been going to until a fortnight ago, he is now in kindergarten, was badly run with no-one really having time to talk to the children. Latterly, he was, of course, amongst the eldest children there, which cannot have provide much incentive to him to do any speaking.
Thanks again for your interest.