Children often want things passionately and become very upset when they are disappointed. Children with autism seem more passionate than most children but we can help any child learn to cope with disappointment. Here is one strategy: Use simple, consistent language.
When children with autism are stressed, they are less able to understand language so when a child is upset use less language not more. I often use the phrase Sorry, bad news while shaking my head sadly. I don't vary the way I say this, and soon children know what it means.
Using this phrase helps me as well as the child. It helps me see the situation from the child's perspective . The key to staying calm as you tell a child no is to simultaneously see the reality from the child's perspective but also know that the child will recover. Sorry, bad news seems to capture all this and I can be genuinely sorry that I can't give the child what he or she wants but also aware that we all get bad news every day and we recover from the disappointment. I don't feel swayed by the child's intense feelings because I know this child needs to learn the skill of coping with bad news.
At the same time, Sorry, bad news helps the child. It comes to be a phrase that the child comprehends and trusts to mean the same thing every time.. He or she will not like it but will know that once this is said, there is no point to arguing. A long explanation for why a child can't have a thing or do something is an invitation for the child to continue to try to persuade because maybe, in all that stuff you said, there was a little opening for negotiation. Sorry, bad news, after it is tested several times, simply comes to mean Absolutely No.