You rank well on Google for searches like:
childminder in Watford
watford childminder
So your webpage should with luck be visited by parents who use Google to search for a childminder. Therefore consider adding more information to your website. Add at least all the information you list at ChildcareLink, but better still add additional information, photos of rooms etc.
Took me a while to find you on ChildcareLink. First tried Watford and it asked me to select East, South or North. I tried South (as looking on a map, Oxhey looked to me to be South of Watford). You were not listed. Doing a postcode search for WD19, I then got a list of places, which included Oxhey - under which you are listed. Not sure if there is anything you can do - may be worth asking CIS if they know why you don't appear in a Watford search, but do if a specific postcode area is searched.
How did your existing families find out about you? Where do they live... are they very local to you, or travelling through on the way to work? Analyse your existing customers, to see if you can gather any useful information. Also do any of them work for large companies, would they put an advert on a work notice board, let HR department know your contact details etc.
Map location search suggests that you are not that far from Watford General Hospital. How far away are you from there? Does the NHS Trust childcare co-ordinator have your details? Call them on 01923 217356 Contact name I located is Barbara Leon-Hunt (may or may not still be them, people change jobs).
The Trust appears to provide Childcare Vouchers to their employees, plus has on-site nurseries... so there may not be great demand, but everything is worth a try.