I am suggesting a style that is not so popular on the forum but I found very practical: the reporter bag. It has two seperate compartments so you can seperate your stuff and your kid's stuff in two different compartments. Looking at your choices, I don't know if you would find the reporter bag too boxy (trocadero is another choice but smaller). The strap is fabric and it's adjustable (wide strap) so you don't have to worry about getting it messy. YOu might need to try out in the store.