I do see that cm's dc miss out on some of their parent's attention when they are working, but my dc miss my attention when I am at work too. I had thought I could trust my cm to treat the dc equally when they were with her, and do private family treats outside her work hours (like we do).
You are comparing two entirely different situations.
Your children are not with you during your working day, seeing you give your attention to other children because that is what you are being paid to do.
Your children don't have to deal with their living room/kitchen/downstairs loo/garden etc also being used as their mother's workplace, and thus shared with children they would not choose to have round for a playdate, far less have in their space every weekday, and to have to negotiate various rules about keeping their own special toys in their bedrooms, or share them.
Your children don't need to deal with 'treat' excursions to the zoo or soft play being part of their mother's working day, and hence shared with children they would not choose to spend leisure time with, and whose parents are scrutinising the set-up for evidence of preferential treatment.
With a decent childminder and from what you say, yours is the last thing you need to worry about is that her children are having a wonderful time at the expense of yours. It's far more likely to be the other way round.
Frankly, while it's far from unusual, obviously, for childminders to have young children of their own, it's often no more fun for their own children than it would be for you if your husband started a business that used your kitchen and living room from 7 am to 6 pm daily.
I regularly look after a friend's dc and I would never dream of taking my dc put for a treat while the other dc watched
But your childminder did take your children out for a treat, along with hers. The treat was the day out at the activity. In addition to that, and unusually, she chose to buy her child something, or we don't know to allow her child to spend pocket money/birthday money on a bear kit, which the child then made at home. In her own house.
but this is a situation where one particular child will get while they always won't
This has happened once. Once. Apart from a zoo trip where her child was bought a cuddly toy, a full year ago. Numerous other trips have involved her asking you to send spending money with your child. And you say that you are very happy with this childminder, and that she has an excellent relationship with your children. Are you really precious enough to stop sending your children to a childminder you say is excellent because of your ungrounded fears they are being sidelined for her own child?