The average price parents shell out on their baby’s 1st birthday party is . . . $293. For comparison, the average Sweet Sixteen costs $280 . . . while parents spend $229 on 10th birthday parties and $226 on 5th birthdays. One of the big expenses for a first birthday is a personalized cake, and social media probably plays a big role in that. Other big-ticket items include: New clothes, “balloon arch” decorations, party props, and a children’s entertainer.