Also in my case (where my son at nursery alleged that he was hit by his dad - but then also said the same of a Male nursery worker so it was dropped) another thing that we did wrong (in hindsight) was we used to be very generous with the staff.
We both worked full time we didn't have family and so we were so grateful of the excellent carers so we used to prioritise them for Christmas and end of year gifts.
I am a pretty generous person and like to give gifts to show appreciation.
Apparently this looked like we were trying to buy them off from any concerns.
I only found this out much later I used one of the staff members as a baby sitter for my children.
Anyhow it certainly made me think.
What you might be doing may be viewed completely differently.
Also something which really concerned me at the time of the allegations was how do we prove it wasn't correct.
I mean we didn't want to try influence our son.
Also we were both so busy working that any spare time was spent on our children and we were not particularly social at that time in our life, firstly as couldn't afford it and secondly family was really treasured.
To be honest with the op should be truthful but again I don't know about being open.
I am afraid I would see the social worker as someone who obviously needs to do their job and I would be truthful but I would also try to manage the situation so any concerns are dealt with.
As such I would not offer any medical history unless it really was relevant.
I would not be defensive but again obviously a social worker can hold power so I would be wary of that.