That should be ok. All subject to the above-mentioned safety requirements, of course. But I still don't see why you can't use a simple non-electric valve, which would automatically open when the bottle pressure dropped. Or are you trying to control the valve and so control/measure the amount of liquid the infant drinks?About the supply with these above components would it be ok to consider:
1) a 5V supply for the sensors and then with voltage regulator going down to 3V for powering the PIC?
2) using a separate battery just and only for the valve?