Hi Bethylou, the test for children with DLA is whether your child needs "Substantially more care, attention or supervision than a child of the same age without disability".
Low Rate Care is awarded when the Decision Maker is satisfied that the child needs at least an hour per day of additional care, attention or supervision.
The fact that the diet is expensive is irrelevant, as is the cost of the appointments you take your DS to. However, the time that it takes would not be irrelevant.
It is crucial to realise that it is the impact and consequence of his dietary needs that would be relevant to a DLA claim, not the dietary needs themselves. So what you need to consider is whether the combined care your child needs is over 1 hour per day on most days.
To be successful in a DLA claim for him, I would imagine he would have to be quite severely and chronically affected by his intolerances with lots of time consuming preventative measures.
The closest example that springs to mind is eczema. One child could be eligible for DLA if their eczema weeps, needs extensive regimes for prevention and treatment, such as wet wrapping of bandages 6 times per day, or 3 baths a day, etc. Another child would not qualify if their child was sufficiently managed by wearing cotton clothing and having cream applied for 20 minutes once a day, even if they both have the same diagnosis.