I'm quite pleased that discusting asked how there is a cost element associated with a child's disability.
For those of us with disabled children it is completely obvious, because we live with the cost implications every single day, but for others, even those who are parents themselves, there is little reason to for them to have an understanding of the way in which a disability impacts on every aspect of family life.
My son has a significant, but not highly complex disability. He needs some additional support day and night and has lots of appointments. His DLA just about covers the additional petrol cost to drive him to the specialist speech and language unit he attends. We chose not to use the Local Authority taxi service as the journey would have been over an hour each way (at just four), alone with a taxi driver (who he might not know on any particular day). That for us was a safeguarding concern and we chose to use the money to dive him ourselves.
While the DLA covers that, it then cannot cover the reduction I have to take in hours to be able to transport him (I can only work 5 hours a day), the cost of my daughter's before and after school care as I can only be in one place at a time, travel costs to several medical professionals, specialist equipment such as shoes, a special toothbrush, flavourless toothpaste, a babysitter with some SEN experience, weighted blanket and mat, replacing items that get broken when he has a bad day, one to one swimming lessons, resources to help with OT and physio activities, travel costs to SEN sports club 15 miles away, unpaid leave in the school holidays as he can't attend mainstream holiday clubs.
That's just off the top of my head, I'm sure there's loads more I haven't thought about. Today my parents (in their seventies) have kindly driven an hour and a half to look after him to I can get some work done.
And that's a child with less severe special needs. Children with more complex disabilities need care day and night. There is not one aspect of life, or how money is spent (holidays, groceries, childcare, housing, clothes) that is not impacted by their disability.