My daughter is nearly three. Quality fur-lined winter boots cost as much for her as they do for me. Only difference is, I don't have yet another growth spurt and require a new pair after only six weeks.
Mostly, it's the little things that add up.
For example, the amount of colouring books, crayons and so on the girl gets through simply astounds me. The odd Kinder Egg, stickers, a soft toy from the supermarket just because it's payday. No, none of those things is strictly necessary, but you are going to want them for your child, I promise you.
Food expenses for her are quite high. She will refuse roughly half of whatever is offered to her on a given day and require something else nutritious.
Electricity bills from heating whichever room she deigns to fall asleep in, leaving the hall light on so she doesn't get scared if she wakes up, running a TV or computer constantly, having her electric keyboard plugged in for round-the-clock concert recitals...
Clothing is a huge cost where we live now because we don't have lovely English charity shops all around us.
Replacing the stuff they break is also expensive. For example, when they pour a sugary drink all over your brand new laptop. cries