Hi, when do you think is a good age for kids to start learning numbers?

I start both my kiddos really early around 6 months. Mostly just flash cards. Normally, when there is a chance I will just point out things to them, like for example "look ! You have 3 balls" "there are 2 dogs over there" gradually they will understand without much difficulty. My daughter is now 3 years old, she can do simple addition. Most importantly is to make it fun!