Lights, Camera, No Action?

My youngest child is an extremely fast crawler. He may never walk, but he could win a crawling contest any day of the week! For this reason, it has been difficult to get quality, blur-free pictures of him in low light settings. He is fascinated by our back door which has a giant window in it. He loves to watch things outside, bang on it - sometimes with hard objects (yikes!), and of course leave bits of leftover food and saliva in swirly patterns on a regular basis. Needless to say, this door has provided some amazing light for photographs!