Birthday toddler

I read somewhere that children can only remember after the age of 3 years old. Celebrating birthdays before they can remember is a way for us to keep them as memories together. So why not? My twin niece & nephew are 4 and they can remember what happened the week before and even some outings they had a few months back because they would be describing the exact event that happened. But they don’t know how to use the word “last month” or “last week” etc. They would just be saying “yesterday” or “that day”. Hahaha. 😝