Screen Lock App While Playing Video ?

I sometimes let my 1 yr old watch one of her shows on my iPhone, or iPad, but she has figured out that if she touches the screen, she can interact with it. I've been looking for an app that will run in the background while video is playing that would shut off touch screen input until you press some odd combination of buttons, you know ? Like vol up, vol down, home & then you can get back in.
Seen anything like that ??? Thanks !