Will he accept a caution?
Will she give evidence?
Did anybody else see it?
Ok. Then probably they will be able to prove it.
No comment interviews are usually the right thing to do if there is no defence available.
However, here they might offer a caution. They would not normally for a sexual offence but he is a young child and so they might consider it appropriate.
There is no way of predicting that in advance. His solicitor will have to negotiate with the police at the station.
They are not going to be keen to prosecute this.
I wouldn't say anything about ADHD or aspergers. Generally police officers will think that is a load of nonsense and will perceive it as an excuse. Not all officers obviously but quite a sizeable majority consider things like that to be an excuse. Also, in fairness, there are people who do use disability as an excuse.
Overall though I would try to secure a caution.
Can I clarify anything for you?