Simply the act of enabling JS within the browser is enough to have your privacy violated in thousands of different ways and data sucked up by everyone who wants it.
Simply by installing an app on your smart phone you invite SDK's that are happy to report back all the information the OS freely allows access to because why not? Data storage is cheap and collecting that data is free of charge.
But yes, data about children is collected in the millions, and the truth is there is no possible law that can prevent this from happening because it will happen anyway. One example: If FB detects a baby photo you upload, should it be deleted? I mean that baby cannot possibly consent, and you'd have thought the GDPR or some law meant uploading baby photos is impossible, but that's not the case, FB/Google WILL perform facial recognition on that baby.
Your data will be processed, used, sold and manipulated for as long as you generate it.
The GDPR helps, a little, in some ways, but it's really had very very little effect overall (apart from some damn annoying "we respect your privacy" pop-ups on websites).
If the GDPR was serious, it wouldn't be possible to collect this data at the OS level, like, at all, JS would return nothing, Android apps would return nothing (or fake data, at least).
But the GDPR is not serious, at least in some ways.