Dudley and harry are about the same age? then how many kids do the Dursleys have?

Question

I got this quote from a web site that seems to indicate that there are more than one dursley child so where is the other child?
"You couldn't find two people who are less like us. And they've got this son - I saw him kicking his mother all the way up the street, screaming for sweets. Harry Potter come and live here"
this child seems to be a lot older than harry because harry was a baby this kid was walking and kicking? what gives

please read my question before you answer it pertains to book one

Answer 1

I think there is only Dudley. He could very well be quite a few months or even a year older than Harry. Don't forget that babies change and grow up quickly so it is possible for Dudley to have been walking and talking when Harry was a baby.

Answer 2

Well as far as we know in the books so far...... The Dursleys only have one kid. We don't know if J.K. Rowling is going to add another kid in the next book... she might.. she might not but for right now there is only one Dursley kid.