Look at contact a family you can download leaflets that explain
they will want to know what help you think you need eg help to stay in work, a break from caring, siblings needs, what behaviours you struggle with eg sleep, diet, tantrums etc
they must do 2 assessments one for you as a carer and one for the child - they often don't do one for the carer!
often they don't have services for young children or say a young child will need alot of care anyway so you need to say why the needs are above what you can manage eg sleep deprivation, impact on other children, relationship under strain, feeling depressed, health suffering as can't exercise / get to dr, can't leave child unsupervised to do cleaning etc
they will refuse help if they think you can get help for free eg from family so they will ask you where your family live and if they come over or what you would do in an emergency
Think about what you would use money for - DP can be used to buy in help / sitter etc, for extra support to access leisure activities, for after school clubs or holiday clubs
They should not refuse help by saying your child is not disabled enough but often do - they should look at the whole family situation not just the child's label
If you have found it hard to get a sitter etc say you will need to find someone specialist / use a specialist agency etc anything that makes it clear you have additional needs over a family with a child without SN