Debbie's right. But I think you can expect that the advance on an early reader or chapter book is going to be on the lower side of the scale unless you're already a popular author. There's also the illustrator to consider, especially if it's heavily illustrated. I don't think you would split the advance in half, as with picture books, but it's something to keep in mind.
Also, remember that the advance goes against the royalties you'll earn. You have to earn back the advance in royalties before you begin to see checks again.
All that said, I've "heard" of advances as low as $2,000 and as high as $7,000 in these categories. Another thing to remember is that you don't receive the advance all at once. Typically it's split in two or three portions. A check when you sign (which can take up to 2 months from the date you agree on a contract to the date you actually receive one), and a check when the manuscript is submitted and totally finished, as in, ready for the copyeditor (that can take 9 months to 1 1/2 years, depending on the project and the editor's schedule). If it's split in three the next check would usually be issued upon publication.
Going with a strong publisher for this age range is helpful because you get access to the school and library market. It's very difficult for indie books and smaller presses to break in without spending a ton of marketing money and a lot of time figuring it all out.