I can offer an opinion based on having been the wife of man who had an affair (fortunately no children produced from it)
I was devastated when I found out - utterly utterly devastated to have been so betrayed on such away. Your wife will be hurt beyond anything you can imagine by what you have done - the affair, the lies the years of deceit. the child is almost incidental.
I can't speak for your wife, but I feel for her as I know if she finds out she will feel her whole world has come crashing down.
Be prepared for the fall out if you tell her. She will never trust you again. Never. She may find you quite repulsive (I couldn't stand my (now ex) husband to touch me or come near me when I found out. She may very well decide (as I did) that she doesn't want to waste any more of her life with someone who is deceitful and who is capable of hurting her so much. She may file for divorce. Be prepared for all of that and more.
As for you adult daughter - I have an adult daughter and son. They are all disgusted by my ex's behaviour even now more than 3 years on. My daughter has virtually no contact with him, by son very minimal contact. Because when you do something like this you change everything they thought was true about you - they question their whole lifetime of memories with you because you are not the man they thought you were. You are a stranger who is capable of a huge act of betrayal.
Be prepared for your daughter to feel this way (she may not,but she may)
As for the child - , my children have expressed having no interest at all in any children (half siblings) my x husband may produce in the future (He has a new partner now, that he met since his affair and our divorce - but my children have still said they are not interested in any future siblings. Of course this is hypothetical and may change if it happens)
The little girl in Poland is innocent in all this and it may be that in future years your adult daughter may want contact - that is her choice.
There is never a good outcome from these things, never a way in which people won't get hurt. If you leave it and your wife out lives you she will find out when you die, she will be similarly devastated at a time of grief.
Your wife may well have an inkling - whatever you may think - in my experience the lies start to contradict each other and suspicions are aroused.
I hope you find a way forward that causes the least distress to your wife and adult daughter - but I fear that is impossible.
One thing - if you tell her be honest with yourself, think deeply, are you telling her because you genuinely think she would be better off knowing or are you telling her because you are finding the secrecy so hard to deal with ? Don't tell her just to relieve yourself of a burden. For once, put your wife and adult daughter first and think hard about what is best for them.
*So, when she invited me into her hotel room I said yes. And I should have said no.
But I cannot regret it because I love my little 5 year old daughter so much and cannot imagine life without her.*
If you tell your wife please do not say this to her - it is awful, and will destroy her.