well being a parent and having illegitimate children are kinda different things
One implies that they are not a part of your family and are ignored
Now if you said you had children with someone who wasn't your partner and didn't live with you, but you financially supported and tried to be involved with their life and upbringing...well that is different and don't think you would be refereeing to that kid as illegitimate
also, I wasn't going to say it, but I was a witness to that virtual impossibility