Light is key, as is the setting. Get those right and you will be fine. I like 50mm or more on a crop sensor for portraits but you could make it work with wider. You can’t control a baby (nor should you try) so try to control as many of the other things that you can (lighting, setting, props, background). Love the window suggestion that others mentioned if you don’t have access to other lights. In the end it’s just like everything with a baby, have fun and enjoy the time and it will turn out just fine.