kindergarten: ~5 years old
pre-k: 4 years old
preschool: 3 & 4 years old (some preschools accept 2 years old)
under 2 years old usually call Daycare.
要唔要一早報名? Depends on the school and your location. Some schools are more popular than others. You can call the school that you like and ask if there's any waiting list/application deadline etc.
要唔要一早報名 I think is really depend on the school you want to send your kid to. Some have a very long waiting list, so I already put my 2 yr old son's name on their list before he was 1.5 year old last year. However, some school told me to go back to 報名 6 month before school year start.
in US, only 1 yr for kindergarten. before that it's called preschool or day-care.
for public schools, the kids have to be at least 5 by Dec 2 in the same school year (i.e. approx. at least
4 yr and 9 mo. old when school starts) for kindgergarten.
same for most private schools, but some private schools make the cut-off date even earlier to Sept. 1 (i.e. has to be at least 5 when school starts).
for public schools, usually it takes priority applications from Jan to Apr (for the coming Fall) depends on school districts. of course earlier priority go to the siblings of the current students first.
for private schools, if the school offers preschool, their preschoolers can usually go straightly to their kindergarten (unless the kid is not really ready).
if the private school starts from kindergarten (does not offer preschool), mostly they start to take application from the Oct. before the school year til Jan. and the kid will be invited for couple rounds of screenings (and maybe parents interview). then the acceptance letter will be sent out end of March to let u know if the kid is in or not.
however, some private schools take students any time throughout the year as long as space is available and the kid has passed certain criteria.
so, i guess you don't need to worry about kindergarten until yr kid is 4. for now, u should look for a preschool/day-care first if u decide to send yr kid to preschool when s/he is 2.