Today, one of my classmates shared that she attended a 돌잔치; a celebration in honor of a baby's first 100 days. I believe that it's customary to celebrate a baby's first 100 days (rather than a baby shower or birthday party) because back in the day, surviving 100 days was a big deal. That's just my guess.
The teacher told us that traditionally, people give the baby a 24K gold ring or necklace. I thought it was rather odd, until she pointed out that it is easier to hold onto gold, while it is tempting to spend the cash. The family will likely hold on to the gold until the child goes off to hagwon, or maybe until mama needs a new pair of shoes.
These days, gold is quite expensive, so many people choose to give money (around 50,000 won) or baby clothes.