I have a 18 months baby she kneed me in the middle of stomch and I'm 16 weeks pregeant is there anything I should watch for or do

Baby is well protected. You usually would have to experience a pretty significant blow for there to be concern. If you were to have any regular cramping, severe pain, or bleeding then you'd certainly want to be checked.

For the peace of mind, you can always inform your doctor or midwife.