Primary school

Kids typically start elementary school when they are 6.

Oh wow, thank you. My son started nursery school when he was 3 so that will be a big change. Lindsey 😊

Nursery school is not part of elementary school system. Nursery schools in the States accept children at 3.5 years. For even younger children, there are day care centres (crèches in the UK.)

Nursery schools are private schools, while elementary schools are public schools.  (The term public school in the UK means private school in the States.  One doesn't pay for public school in the States, while it's the opposite in the UK.)

Forgot to mention that "elementary" is the same as "primary". 

Nether of your children will be of primary school ages for a while yet, but you can put your younger one in a combination program of day care and nursery school anytime after you move to the States.

If your older one's birthday is on or before Sept 1, he can enter kindergarten the year he turns 5.  Before that, or if his birthday is after Sept 1, he can attend pre-kindergarten.

First grade is the first year of primary/elementary schools. He'll need to be 6 on or before Sept 1 to be in first grade that year.

The North and Northeast areas of Tallahassee have very good schools.

In Thomasville, Jerger Elementary School near John Archbold Hospital is a great school.

Kindergarten is at age 5, the age Elementary schools (primary schools) start. Legally all students are free to attend public schools for. Programs vary from  1/2 to all day depending on state and school district. Many public schools offer full day with tuition for the second 1/2 of the day. There are also private schools that will start accepting students in prek as young as 3