To be a childminder you have to take 4 different qualifications at minimum before you can even apply. It is NOT a job without training. This is at minimum. Once you are qualified as a childminder, you are expected to continue your studies and take NVQ level 3 and beyond.
To be a childminder you have to do a lot more than filling in health and safety forms. You have to learn all the areas of the Early Years Foundation Stage and plan and prepare for each child on an individual basis. You have to observe the child against each of the areas of the EYFS and take notes according to their age and age/stage and them as an individual. Then plan and prepare in relation to your observations ensuring that each child is developing in each of the EYFS areas. Each child has their own individual plan that you have to prepare for and evaluate on a regular basis.
Like a teacher, for everything you do, including just the school run, there has to be a fully completed health and safety form. Just like a school, there needs to be parental consent forms for trips out etc.
A childminder has to put together a pack of information that is to be handed over to the school or next childcare setting. It is a lengthy document that can be held against you should anything be amiss.
There is utterly no difference in what an infant school teacher has to do for each child, and what a childminder has to do.
For each and every child you have, you have to do this work. This is why it is not a nanny share (a nanny is no OFSTED registered).
Also, whilst a childminder may have 3 or 4 children, it is rarely at the same time. On a Monday they may have 2 children all day, on a Tuesday have 1 child in the morning only, on a Wednesday have 2 children in the morning and 1 in the afternoon etc. The doubling or trippling of the hourly rate depending upon the number of children etc is not across the whole of the opening time.