We used to share our first nanny. The second family we shared with were just like you. They specified that their PFB son was only to have unprocessed foods.
Nanny was looking after two 5 month old babies from 8 until 6.30, 5 days a week.
The mum also insisted on ringing every day to find out what they had done and what had been served for lunch.
I was working at home one day - they were based at our house, because their house was off limits. Seriously - her own son was not allowed in some rooms in their house - and heard my nanny say to her "yes, he had a lovely lunch, he had fish, potatoes and peas".
Mum was very happy.
I knew, though, that they had eaten fish fingers, Smash and frozen peas!
OK, our nanny was probably wrong to do/say this, but please - be realistic in your expectations. If you're not there all day doing the work, and if the CM is looking after other children (which is more than likely) then please cut her some slack.