I'm not a parents yet but I do helped my mom to jaga anak.
Mostly those kids that my mom jaga, they will go preschool at the age of 5.
And pls keep in mind, if ur child is 3, the immune system still weak and if one kid sick, whole class also will get.

That's what happened to my cousin's son and she ended up stop him going to preschool and my mom took care of him until he's 5 and he go back to preschool.

Just my 2 cents.