...Easy. Take a deep breath.
You have done well to go into such deep introspective thoughts about yourself. As good as it can be, to get 'real' about one`s self, when we do those things, sometimes we come out of it with even more questions, then we had going in.
You need to take things step-by-step & day-by-day. Do not worry about things over which you have no control in the here and now.
This doesn`t mean 'forgeting' about children. It means making sure you are open and honest with potential partners, that you do, indeed, want children. Right now, thats all that really needs to be known,...even to yourself.
Once you have the partner(s) you desire, you will then either have your questions answered just by knowing the people in your life, or, you will know specifically which questions need to be a addressed, and how to go from there.
For right now though, you are trying to answer questions in the present, that cannot be answered until you get 'there.'
Do yourself a favour and dont let your mind overwhelm you with the sometimes daunting road of polyamory.
Keep it somewhat simple, and let things reveal themselves, as relationships take shape.