goign through this myslef...
with my husband. When he and his ex split (they weren't married) she went after child support. The judge asked him in court if he denied that these were his kids and he said no. BUT from what our lawyer told us, that doesn't mean that parentage had been established. We are still waiting on the lawyer to see what he finds out.
What we have to do if it hasn't been established is get the affidavit thing you are talking about, send it to Bio-mom for her to sign then file it with the courts. That will establish parentage. If she doesn't sign it (just to make our lives h**l) then he would have to get a paternity test to prove he was the father.
So your affidavit thing, according to our lawyer, would be an appropriate way to establish parentage legally. However to get visitations and equal rights legal (and trust me, you want to get it through the courts incase Bio-mom turns bitter someday like ours did) then you and she just write up a parenting plan (since you and she seem to be on good terms right now) with shared custody and file it with the courts. This would make it legal and if something ever went awry in your relationship, you would have legal rights to visitation and she would have to go to court to change that. I would get a couple free consultations with a lawyer to get it written up right. You can also find examples at
www.deltabravo.com in the Articles section.
Best of luck to you. I hope you get everything worked out.
Also, in regards to the Illinois FAQ quoted above, I feel that it is total bulls**t that a father only can claim to be dad up to 2 years, but bio-mom has the right to do what she wants up until age 18. Just goes to show you the biast in the system. They just assume that bio-Dads are dead-beats and don't take into consideration the extreme lengths that Bio-moms go to sometimes to keep Dad out of their lives just out of pure spite. I am a Bio-mom and a Step-mom and have seen both sides of the plate through-out my life.
Ok, off my soap-box, just a little emotional right now. My little girl started Kindergarten and I haven't got to see my bonus-boys since Christmas because their bio-mom decided they had better things to do this summer

Emotions run high in this house right now. Even though they are not my bio-kids, I miss htem as though they were and it really hurts
