Firstly, PIP isn’t paid to children under the age of 16. It would have been child DLA which switches to PIP at age 16. Child DLA is particularly difficult to claim. All children are dependent to some extent, but for child DLA you have to demonstrate that the level of age related dependency caused by disability is beyond the expectation of that of a child who is not disabled. To then make a successful claim for PIP, once DLA ends, you have to demonstrate that to a much higher standard, because the criteria for child DLA and PIP are very different.
PIP looks at the level of disability caused by the condition and the effects on daily life. It does not, and has never, assessed capability for work, and payment of it is regardless of whether the claimant can work or not. The award of PIP is intended to cover some of the extra cost that disability brings about and it’s a very difficult benefit to claim, despite the general MN attitude that DWP hand these awards out like sweets.