According to scientific research, the average person starts forming their memories when they are 3 or 4 years old, but those memories get erased as time passes, opening space for new memories to replace the old ones. There isn't a exact number, but that's the case for most people. Some people can remember stuff from when they were 2, some people can't even remember stuff from when they were 8. This number varies depending on the person.
According to the same research, a few memories of the children get crystalized when they reach the age of 10, but not all of them, only the important ones. So it makes sense that Sarada remembered that memory with Sasuke and Sakura.
@Bold: where did you get that from? I don't recall the manga ever stating that. It only says that a Uchiha has to go through emotional trauma to awaken their Sharingan and evolve them.
Another scientific research states that a baby is able to recognize their parents almost immediately since birth. When Sarada was born, Sasuke was there. He actually spent Sarada's early years of life with her. By 3-months-old, most babies know the difference between familiar faces and strange ones. Sasuke spent 3 years, at least, around Sarada - that's more than enough to create emotional attachment, especially considering the fact that your child will be able to recognize you after 3 months after birth.
When is NaruHina is not filler, but when is SasuSaku it is.
Talk about hypocrisy. smh :lol
