Yes, but the gran was with this man for 5 years.
He had a criminal record - but not for sex crimes.
Plenty of reformed criminals out there. In fact, even amongst hardened criminals, paedophiles are seen as scum, that's why they get so much protection in prison. These perverts gain access to kids because the parents trust them, happens at all levels of society. He could have done a good job of convincing the gran he was a reformed character or a lovable rogue. We just don't know.
Seems to me, that lot of assumptions being made about the mum and gran just because they are not boden clad middle class professionals. Where is the evidence they were druggies, a chaotic family or that social services were involved? I haven't seen that, or is that something I have missed?
Red flags and awareness of grooming are an important thing to raise awareness of, but there is no need to single out individual cases, especially not a bereaved family.