Step daughters/Asexual/1st Wednesday/play room/Keep pushing
Well, might as well go the full mile, you've already come this far, right?
You blow a few more raspberries on Sandra's belly, and then give her a quick kiss on the forehead. Now then, how to convince her? Well, you might very well be able to just ask at the rate things are going here.
"Hey Sandra." You say. "Can I remove your underpants?"
Her eyes glance down for a second, and then she groans. "My mommy says I'm not s'posed ta show my privates to people." She says.
"Well, I've kinda seen them already when we were in the shower, didn't I?" You ask. "It shouldn't be a problem if I see them now, it's just like your mom seeing down there, it's no problem."
Sandra seems more than just convinced by your reasoning, she only seems to pretend to think for less than a second before she has a big smile. "Take them off!" She says with a huge smile. It seems like she really likes being undressed by you for some reason. Well, let's not argue with the little lady. You reach down and pull her underwear down as she lifts up to help you, bringing her slightly parting pussy lips and a plain view into her pink insides as you pull her panties down to her ankles, and then she allows her legs to flop open as soon as her underwear are clear of her feet. She seems a little nervous, but you can tell from her face that something about this is actually exciting to the little pre-schooler.
Now she seems pretty eager to know what comes next.