Most Helpful Guy
Depends on how things are going. Whether you think this will be long term, etc. If it is more than friends with benefits then once you both feel secure with one-another then it may be good. However, it may be fine anyway as long as you met the child as a friend of the child's dad and you guys aren't all mushy and touchy around eachother in front of him.
If it were me and my child I would let you meet at this point but call you a friend and keep the affection at zero around the child. Just act like any other friend. As the child gets to know you and feel more comfortable and as your relationship strengthens then maybe you can ramp that other stuff up.