What can you teach a 3 month old?

I watch my 3 month old niece on Mondays and Wednesdays and I really want to take an active approach in helping her develop. When I put her down I play classical music or a baby einstein dvd and after I feed, change and burp her I read to her, but I want to do more. Unfortunately, I’m no expert in child development but I figured someone else out there was so whats up? What can I do?