That's true in many other states, as well, but it really doesn't matter. To some extent, simply signing the document indicates agreement. Notarization simply makes it harder to say "I didn't sign that - it must have been someone else".
For OP's benefit, a notarized agreement is useful only in a limited number of circumstances. It is certainly never going to override a court order. You can forget that right off the bat.
It is NOT going to be very useful to try to convince a judge to change custody, for example. The person who signed it could say "yes, I did agree at that time, but since then, I've changed my mind and I don't think it's a good idea" - which would make the agreement almost useless.
About the only place I can see it being useful is where the couple signs an agreement for 50:50 custody and then one of them changes their mind. If they try to tell the court that the other person is completely unfit and a danger to the child and should never be allowed anywhere near the child because they have ALWAYS been a terrible person, the signed agreement would absolutely weaken that position. The opposing attorney would simply ask "if this person is so evil and terrible, why did you agree to 50:50 when you signed this". Unless there was a gun to his/her head, it's hard to answer that (and, obviously, a notary would probably not notarize a document signed under duress. If the gun was also pointed at the notary, then there should have been a police report filed).