My son was born with one small (.4cm) cafe au lait spot. he is 5 months now and i think i see another small one. is this likely nf1?

Probably not: We want to see at least three cafe-au-lait spots. A tiny one which you only "think you can see" isn't necessarily a cafe-au-lait spot. Suggest you check it out with your son's pediatrician at his next scheduled visit. I certainly would not panic nor set up an appointment just for this. It probabably isn't.

May develop later: Symptoms of nf1, which may be evident at birth and nearly always by the time the child is 10 years old, pigmented, light brown spots, six or more measuring 5 mm in greatest diameter in prepubertal individuals and over 15 mm in greatest diameter in postpubertal individuals, freckling of armpits, nodules or neurofibromas, 2 or more, two or more growths on the iris of the eye, a tumor on the optic n.