Got DS (18m) ready to go out with my parents, suddenly noticed in the kerfuffle of getting carseat etc ready that his trousers were wet down the front, and it was a shape like when a child wets themselves.
Impossible I thought, DS is in nappies, and it hadn't been that long since I'd changed him so it wasn't a case of saturation.
Stripped him off and it turned out he'd managed (somehow - he was wearing baby vest, trousers and t-shirt!) to tug his pull-up nappy down and tuck it under his willy so the wee had just gone everywhere... EUWWWWW! Have to admit I'm still PMSL at the sight of it peeping over the top though 
I'm sure DD never did anything that gross 