Nice work so far @wint0178, great that you try expanding on the examples. Sorry for the late reply. If you look at https://github.com/mysensors/MySensorsArduinoExamples/blob/bba998bce09bc5139eb4ca7a05b0279f4083ff88/examples/PressureSensor/PressureSensor.ino#L90 you see where the existing child ids are defines. You just add another one for the gas sensor, with a unique number (incrementing by 1 is an easy way). Try that and report back on your result. If something is unclear, just post a followup.