When my son was about to pop out, I bough a 50 f/1.4 (for him, not for me :-)). It hasn't let me down, although on my crop body, it is sometimes too long when doing indoors work (which you will be doing a lot with a newborn). For example, it worked nice for the first shot bellow, but for the second I had to switch to a wider lens, although I brought the ladder inside and climbed all the way until my back was pressed against the ceiling!
Based on my experience, I would recommend against the 85 on a FF, but certainly for a 50. Your f/1.8 might work well, but the f/1.4 is not going to break the bank and will improve your depth of field and bokeh.
More importantly though, I would strongly encourage you to invest in some lights, if you don't already have some. I would argue that the difference between nice light and random light is bigger than the difference between the canon 50/1.4 and the otus. At the very least, buy a cheap diffuser/reflector (or a not so expensive and practical one like this: http://www.bhphotovideo.com/c/product/283648-REG/Impact_CRK_42K_42_5_in_1_Reflector_with.html
If you don't even want to invest $100 in lights, build yourself a large DIY softbox. The internet is full of advice on how to do that for next to nothing.