When I searched on PubMed, most papers analyzing the hair follicle test for cocaine affirmed that the test is good for determining if exposure to the drug happened in children. However, it isn't a very reliable test for confirming the dose the child was exposed to or for how long.
I know that 10x the reference value seems very high, but it really depends on the tests. Some tests consider 10x the reference value as nothing, while others see 2x as a huge difference. So, I think it’s better to leave this kind of analysis to people who really understand the interpretation well.
I would trust
@AltisticRight opinion on this.