Is data protection. They have a different set of obligations to children under EU and UK regulations than they do to adults and in not identifying which is which on their platform they are entering a fairly interesting situation regarding their legal responsibilities. Given that they clearly make no efforts to verify the age of players (as stated by Pence in the hearing) they are most definitely in breach of EU data regulations.
Of course, whether or not the UK can do anything to inspire the EU to take action, right now, is something of a pertinent point in terms of whether or not this practically goes anywhere but.... if it is taken up as an issue the level of fines can be eye-watering.