We want to make his polish passport
It would be best to contact the Polish Embassy, but in order to get a first Polish passport, you will need a Polish birth certificate, and PESEL number. Your child will have to have his birth registered in Poland. I am fairly sure that if you have an English birth certificate for him, then it's possible to get a one year temporary passport here in the UK, but after that you will have to make that trip to Poland.
Here is a link to further information: