I have been doing a lot of youtube and google searches for cakes and I have noticed a lot of people are painting very lightly (like the baby mold you can get) to give a little color to their fondant.. I was wondering how this was made??

When I paint on fondant I use airbrush food color. Some people mix petal dust or gels with an alcohol (vodka or some sort of clear extract). The "Rock Star" cake in my gallery, the zebra stripes are painted with a black airbrush coloring.

I use gel coloring with lemon extract...or vodka if I want it to stay wetter longer. I painted the spots on buttercream on this leopard cake I did. If your buttercream is cold and hard, you can paint very easily on it. I like to mix my gels with the extract to lighten and kind of work like watercolors. I've never used airbrush colors, but might try them should I do another paint job!
Here's that cake I painted: http://cakecentral.com/gallery/1998796/leopard-print-birthday-cake-for-friend

I love airbrush colors for painting on cakes.

If it is something like the babies, it could be that they are just doing a dry dust using the petal dusts. That would give you a very subtle look.

I use powdered food colors or lustre dust mixed with lemon extract to paint. Sometimes I use airbrush color, too. The sun and moon cake in my gallery was painted with powdered food colors and lemon extract.