My son is 15.
His costs are just escalating every year!
Sports associated fees (uniforms, equipment, travel, treatment of injuries, etc), brand closes and shoes (when he was little he did not care about labels, now is the whole different story when he is in HS!), orthodontist fees every 6 weeks (he is in braces), outdoor adventure summer camp just paid more than 3K (no more park district camps for the big kids!). And a lot more! There is a huge bump in spending when the kids become teens, it is like another mini-adult living in the house, even more expensive, because they grow fast and can only wear that Abercrombie T-shirt for 1 season, the Nike sneakers last about 6-7 mo due to rapid feet growth or excessive wear and tear (toes start to poke out).
The next thing,my son will be 16 and will want to drive. Car, insurance, etc. the list goes on. Then there will be college.
Brace yourself! 10 is the good age - enjoy your baby!