Any person in charge of a child under the age of 8 should absolutely, without question, be responsible for attending to all of their needs.
There is no safeguarding issue regarding toileting for people who are looking after children in a nursery and in primary school. Apart from time and staff constraints there are no issues regarding helping a child with their basic needs. It might well be policy but that is not law and, as a policy, it stinks. Any nursery or preschool worth their salt will either do, if the child is unable to do it themselves, or teach and assist the child to do it themselves.
It is ridiculous in the extreme to say all 3yr olds can do it, or all 8yr olds should be able to. Children are individuals with unique needs and there is not a blanket approach. And frankly, any person who thinks all 3 year olds can wipe their own bottoms, or any person who thinks helping is a safeguarding issue, should not be working with children in the first place.
As for calling the parent each time, what a totally ridiculous suggestion. Can you imagine the fallout at work when Mary In accounts is called out three times during her working day to go and help her child wipe its bottom?
If it really was a safeguarding issue, or not allowed by ofsted or any other governing body, then there wouldn't be any childminders, or nannys because they are working alone.
It's lazy childcare at best, with nurseries, pre-schools and schools using "best practice" as an excuse to vacate their responsibilities.
And just for context, I have been working with the under 8's for 40 yrs. I have worked in schools, hospitals, private homes, nurseries and for the past 18 yrs at home as a childminder and I have not once called a parent because their child has needed help with personal care and I have never had a complaint made against me for wiping a child's bottom