The requirement to be on a central register could improve nannies' professional recognition, drive up standards and provide protection for children and parents, it says.
The survey of 900 nannies and 55 nanny agencies also found that a significant number of nannies did not have CRB checks.
Seventy-one per cent claimed to have an Enhanced CRB Disclosure, but 29 per cent did not, while 46 agencies said they required all nannies on their books to have a current Enhanced Disclosure.
Just under half of nannies who are already listed on the voluntary part of the Ofsted Childcare Register said registration should be mandatory, and 26 per cent of those surveyed said all nannies should be registered with Ofsted.
However, nannies on the register highlighted areas of concern with the system, such as the cost and complexity of the process.
Some nannies in focus groups reported that post office staff did not check documents such as first aid certificates, CRB Disclosures and public liability insurance, as Ofsted requires, though it was not clear if these were isolated cases.
Nannies also felt the register was marketed to parents as a way of saving them money rather than of ensuring professional standards or protecting children, which 'sent out the wrong message'.
The research was commissioned by the CWDC in partnership with education union Voice and the National Childminding Association, and is believed to be the largest ever study of the nanny workforce.
It also reveals there are an estimated 30,000 nannies in England, 99 per cent are female, 56 per cent are under 30, and 82 per cent have an early learning or childcare qualification.
Voice senior professional officer (Childcare) Tricia Pritchard said she hoped the findings would add weight to the call for a compulsory national register of nannies.
She said, 'A single UK national register for all working with children and young people would be much simpler and more effective than the current complicated, confusing plethora of compulsory and voluntary childcare registers.'
Find the survey.
