Such idea’s are currently being debated in the U.K (Scotland in particular) , A candidate for the Irish presidential election, David Norris, also recently advocated a ‘re-think’ of the concept of consent in juvenile sexual relationships, including the place of older partners.
There is also the separate but related and developing issue in many western countries, where both partners who engage in sexual activity are under-age children but who are now not considered to have violated the concept of ‘age of consent’.
While, as you know, both are Mortal Sins and thus by committing either of them a person turn their back on God and His Church, the moral gravity of the Sin of Child abuse is far greater than deliberately missing Mass; every practising Catholic should know this and be able to make this distinction.
But people will often try to find excuses to pardon themselves, you don’t have to be Catholic to do that.
Any Catholic who attempts to equate Missing Mass with Child abuse is either wilfully and deliberately ignorant or is trying very hard to excuse their own sinful behaviour. either way the objective truth of the matter remains the same as does the moral gravity of the Mortal Sin of child abuse.