I submit that the concept of presumptive atheism comes dangerously close to establishing a belief for atheism other than the lack of belief or disbelief in God or gods, and should be rejected on that basis.
To put it simply, if accepting presumptive atheism is part and parcel of being an atheist, then clearly I'm not an atheist, nor do I want to be.
My personal belief is that insensate beings who are unable to understand philosophical concepts such as god, like babies, cannot be considered atheists and would more appropriately be labeled agnostic. They simply do not know if there's a god or not, and are therefore incapable of hazarding an opinion on the issue.
It is my further belief that small children also cannot properly be considered members of a religion due to their propensity to magical thinking and the fact that they accept what they're told by authority figures. I am certainly in no rush to tell Christians or Muslims that their children are not real Christians or Muslims, though

I personally will only accept a statement of faith or lack thereof from people who have reached an age where they're able to reason, such as their teens.
I think that Catholicism sets the bar too low at setting the age of reason around 7 years old. I can't think of many 7 year olds who would feel willing and able to go against their family and community for a philosophical principle, so a 7 year old is more likely to espouse belief, whether they mean it or not, or have lingering beliefs based on fear of eternal punishment or peer pressure rather than logic and reason.