For the longest time, my son would not touch any vegetables or fruits. So, I resorted to guerrilla tactics by lacing food he already liked with extras he never knew about. My favorite trick, which I still use, is replacing oil in baked goods with baby food. You can substitute the exact amount, but I just pour in an entire 6-ounce jar and no one ever notices! Does it add a lot of nutrition? No, but every little bit counts.
What amazes me is that even though we haven't had a baby around here in years, no one questions why I still buy baby food!