SAL35F18 for photographing baby/children indoors

I'm going to agree with Alphoid that perspective distortion is a real issue and that perspective is determined by the distance to your subject, not the focal length of the lens you are using.  I usually want to be at least 6' from my subject and prefer 10' or 12'.  Of course it's often physically necessary to be closer.

Once at a specific distance I'll pick the focal length that frames my subject the way I want.  Indoors that usually means using 35mm or 50mm, but can be as long as 85mm or 135mm.  When I'm in close quarters it would almost always be 35mm.

I think your choice to go with the 35mm f1.8 first is a good one, but I also think you'll want a longer prime eventually.  I use the Sony 35mm f1.8 and the Minolta F1.7 and I've been very happy with both, although I would buy one of the better 50mm primes if I was buying today.  I guess my point is when you do want a 50mm lens, if money is very tight the Minolta f1.7 works well for portraits in low light, but if you can afford better get better.