I was in second grade... and I figured it out on my own. Santa used a blue pen on his name tags that looked an awful lot like the blue pen my mom used! Even back then I was highly aware of colors and the different line qualities you'd get from different pens I asked my mom, and she had to fess up based on the "evidence" - but she told me not to tell my brother... who figured it out on his own about the same time because he lost a tooth, and caught mom leaving money under his pillow. He reasoned that if the tooth fairy was fake, then so was Santa. No pulling the wool over our eyes!