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Many paints contain additives known as VOC's... volatile organic compounds. They have a variety of functions from being the primary solvent in oil-based paints, making the paint brush or roll on more smoothly and to increasing drying speed.
VOC's don't stay in the paint, but evaporate as the paint dries and are released into the air. They have been connected with some health and environmental concerns so your apprehension, especially around an infant, is warranted.
Fortunately for the health-minded, a growing number of paint manufacturers sell paints that are low VOC and low odor. There is no additive that I am aware of that can lower the VOC level of a paint... maybe mask it, but not lower it. So put the olive oil away and head over to your local paint store!
Interesting solution... brings tears to my eyes! (P.S. I'll have to try this myself.)
Always liked vanilla smell over onion. Wonder which works best? Hmmm. Anyway, you are correct... eliminating odor is one thing. Eliminating the VOCs... volatile organic compounds... from a paint can only be accomplished by purchasing paints with low VOCs to begin with. The effects, of course, can be reduced by adequate ventilation.
Unfortunately, the toughest stain-sealing jobs such as smoke, tobacco and water spots are still best accomplished with high VOC primer-sealers. Water-based products are getting better but still have a way to go... in my opinion.