DH was involved in an accident last year with DD (5) in the car. The other driver went through a red light, and wrote off our car. DH didn't take her to the GP because she said she was OK and he didn't think she'd done any damage, yet she told me months later that she'd banged her head on the window 
DH didn't claim for the car seat on the insurance as his friend had told him it was a faff
.
DD started waking up screaming immediately after the accident, several times a night. That morphed into also refusing to go to bed. We didn't connect the behaviour to the accident at all and got more and more frustrated by it. Then the insurance company asked if she'd been affected and told us that if we didn't claim for her "injuries" she could sue us when she was an adult
. I don't know how true that is.
But they told us we could claim for counselling/ psychiatric treatment for DD, rather than money. They sent us to a GP and a private psychologist who agreed that what she was suffering was classic behaviour following an accident.
It has taken 9 months of endless phone calls and form filling and they have just got back to us this week to say they've agreed to a pay out (not what we were expecting at all) for DD, but we have to go to court. It will be held in trust for her. They will also pay for her replacement car seat.
This has turned into an epic but I wanted to counter everyone saying that because you didn't take your DC to the GP you won't be able to claim. I will also say that ordinarily I loathe this compensation culture and certainly would not be claiming for a non-existent complaint but she really was traumatised for months by what had happened. (But had they told us from the off she would get cash we wouldn't have claimed - we were led to believe we'd get private medical treatment).