You talked about weight gain, in absolute terms. A novice powerlifter can easily put on both more absolute weight and absolute strength in a year than a newborn.
The image of a baby trying to outlift the weights that a novice weightlifter is lifting is now ingrained in my mind.
What I was trying to say is the baby is growing faster. If you stay at average weight throughout your life, like you're tracking along the 50% line on the growth chart, then your fastest weight gain is in your first year. On average that's when you gain the most weight (even in absolute terms), despite the fact that you're much much smaller than, say, a growing teenager.