Photography

If you didn't remove a larger sensor and cut it up and put it into your camera you don't have a 'cropped' sensor. You have a sensor in APSC format, it is no more a 'crop' than a 'full frame' sensor is to medium format sensor. Short people aren't 'crops' of taller people.

At any rate, a fast lens and a focal distance of at least 50 mm has brought me some good success. Pack a lot of patience and shoot a lot of frames. Bounce flash can save you indoors. If that isn't possible, turn up the lights, more than you think you need.

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.

It's not about specific lengths, it's about location.

Get down to their level (good suggestion for animals too) physically lie on the floor if you have to.

Not too close, short lengths make things distorted, 35mm plus is better. Also a longer shot will help provide bokeh in a background with an open (2.8-4f) aperture. Consider what is in the landscape and if the scene is messy.

Patience, your subject will be a crap uncontrollable model 90% of the time. Take lots of pics if your not using flash, burst those shots and disregard all but the occasional good one.

Use the screen on your camera instead of looking through the viewfinder. You’ll get much better smiles out of them when they can physically see your face instead of just your forehead behind the camera.

Soft lighting, and enough of it that you don’t need a flash; babies and little kids sometimes get really upset by flashes. Also, have the parents bring some of their favorite toys they can use as a distraction.

get down low... avoid flash....

go to youtube and search for 'infant photography'