I've described this before... both boys at somestage seemd to go through a phase of believing that excretion was something they would eventually grow out of. I really don't know how they got that idea - with all the kids, they would follow me to the bathroom and watch while I did what I had to do (as an example, as well as my own desperation with a clingy child).
I remember easy child 2/difficult child 2 applauding me one day after I "performed" and saying, "Good girl, Mummy!"
but the boys never got the idea. I'm sure that when difficult child 1 decided somewhere in his head, to not put it in his nappy, but also to not do it in the toilet, tat the problem would just go away.
And then there was the morning with difficult child 3 (he was verbal, so he must have been at least 6). He slammed out of his room, burst through the toilet door like a SWAT raid, made souds like Niagara falls in flood and I heard him say exasperatedly, "EVERY MORNING, there's wee!"
Marg