D.P.
I also have a 4 1/2 y/o and a 2 y/o and my son does the exact same thing to my daughter!! It must be the age. Most of the time he'll talk her into wanting something that he actually wants and then he'll say "Mom, Kaitlyn wants this." He's very clever. I don't know a way to stop it. We do time outs if when it gets really bad, such as him continually asking her if she wants a sweet treat at bedtime right after we brushed her teeth. Other than that, I think it's just his age. It's definitely normal behavior.