There is no comparison really. A cleaner drives in her car to my home, stays for an hour and in that time works solidly for me for the whole hour. £8. She then drives off to another house, making the travelling time at least half as much again as the hour she is here.
A childminder may look after 3 or 4 children at once, meaning that the £4 per hour is increased to £12/£16. She has the ability to work in her own home, and the children will usually be dropped off there by the parent, so charging from the moment they arrive.
I do not mean to devalue what the childminder does, but the earning capacity is not the £4 per hour you are quoting.
Cleaning is 'unpleasant' work, so presumably you are also paying a premium to persuade someone to do a task that you don't want to do.
A nanny who works exclusively for one client would be paid more per hour to take account of the exclusivity?
Another factor is that anyone who works in short shifts like an hour gets paid more than someone doing a long shift. Lollipop ladies, breakfast club supervisors, all of these jobs pay more per hour than one with a 9-5 daily pattern, presumably to make up for the inconvenience of the journey to and from work just for an hour or so.