Having had two children with SEND, I am sick to death of being called Mum by other adults.
When my children have been in hospital and they are cared for by a different nurse every shift, I completely get that remembering my name isn't a high priority.
When I have seen and spoken to the same member of school staff every morning and afternoon for months or years and they know the ins and outs of our family life in glorious detail, it is not expecting too much for them to address me by my name and refer to me in conversations and emails with other adults in the same way. There's no way they don't remember my name and not using it feels like some sort of power play.
When a professional is writing an in depth report about my child and her difficulties, it is lazy and unreasonable to refer to me as Mum.
When I attend a meeting with a group of professionals and every other person in the room is referred to using their name , it is bloody rude and dehumanising to refer to me as Mum, especially in the minutes.
If you're a professional working with children and their families and you can't remember a parent's name, just ask them. Unless your contact with them is fleeting and building a relationship with them is totally unimportant, it matters that you address them politely. Using Mum, Dad, etc when you don't need to is lazy and rude.