Hi @Choran,
This is a very strong candidate for off-gassing. In the case where you’ve not heard of this terminology prior to today, I’ve included a description extracting from a Community article created on this subject.
“Off gassing where a pollutant source is producing a gas at a constant rate over a prolonged period. This source can sometimes be picked up as an odour, and even though the odour may dissipate over time, the source can continue to omit the fumes.”
The coincidentally named article, What is Off Gassing and what is the cause? Provides a further description, expanded detail, an example of the cause and several recommendations to remedy the situation. I suggest referring to it before deciding on a cause of action.
One suggestion I may make, is that following the recommendations on the aforementioned article, you test the purifier in your child’s room near their sleeping location. I would hope you see a noticeable difference.
David.