When to use flash and when not to use flash when taking picture of a baby? Thank you!

My husband was a photographer. He never used flash when taking baby pictures. He used fast lenses instead which has a wider aperture. For portraits, it's advisable to use a 50mm f1.8 prime lens. It's cheap, around 5k for bnew and as low as 2k for 2nd hand. If using a kit lens, better to take pictures with plenty of natural light with matching reflectors for better lighting.