The third link provided by StrongBad is not directly relevant here. That page does not explain the criteria that determine whether a child is a UK citizen at birth. Rather, it explains how a child who is not a UK citizen at birth can register for citizenship at a later date.
Here's the short version: if you have lived in the UK for five years, your child will be a UK citizen at birth.
Here's the long version:
A child born in the United Kingdom will hold UK citizenship at birth if at least one parent is a British citizen or is "settled" in the UK - that is, holds Indefinite Leave to Remain or permanent residence.
As an EEA national (Poland), you have the advantage of avoiding the lengthy and expensive process of applying for Indefinite Leave to Remain. Instead, you gain permanent resident status when you have "exercised your treaty rights" (lived and worked) in the UK for five years. This happens automatically. You do not have to apply or take any other action.
When you have gained permanent residence you may choose to obtain a permanent residence card. This is not obligatory. Getting the card or not getting the card does not affect your status. The card provides proof of your permanent residence status. If you have a permanent residence card dated before your child's birth, the Passport Office will accept the permanent residence card (together with your child's birth certificate) as proof of your child's citizenship.
You haven't said anything about the other parent, but obviously if they're also an EEA national this all applies to them too. If either of you qualify as settled in the UK, your child will be a UK citizen at birth. If neither of you qualify as settled, your child will not be a citizen at birth.
If your child is not a UK citizen at birth but you or the other parent later becomes "settled" (or acquires citizenship) in the UK, the child can then register for UK citizenship under section 1(3) of the British Nationality Act 1981.
(I am not an immigration lawyer. I am, however, a UK dual-national parent of a UK triple-national child.)