Even though people do the 'math' of, 'well, it's a 1.4 crop factor times a 35mm focal length, so that's right about 50mm....', that is not accurate. It's still the exact same distortion of a 35mm focal length.
Distortion is due to the focal distance (except for distortions due to lens design, which is mostly in ultra-wide zooms). 35mm on APS-C = 35 *1.6 FF Equiv = 56mm. Normally this would give little to no observable distortion in adult head and shoulder portraits. But for babies you have to get much closer, and distortion might be noticeable.
I have the 35 f/2 IS and it's a great lens, but if you're doing baby portraits you probably want something tighter. Most baby photographers use an 85 f/1.2 1.4 or 1.8 on a FF camera. That's pretty close to the 50 that you already have (80mm FF equiva.). Move in close to the baby and you should get nice portraits with shallow DOF. If you need tighter, go for the 85 1.8, which is sharp and shallow wide open.