Marina,
I think it will be difficult to find a full day program during our school year that would take your son for only a few months, but there probably would be some. I think you will need to wait until right before you come and then call around to preschools and see if any of them have a spot open. You could also join the parent's league and they provide the service of letting you know about empty spots in private schools and preschools. You can also look into schools that cater to International families. The Children's Workshop is one preschool like this (find it on our preschool page). Also the Lycee Francais and La Scuola di Italia are two others. Lastly preschool alternatives like New York Kids Club may have full day programs that you could sign up for for a few months. Good luck!