If the son is still a minor when the Priority Date is currently then the so can be included as a Derivative, obviously son has to be mentioned in the application
It does seem you focus is more shacking up with your girl friend.
She might want to investigate job prospects in Holland a bit as well in her circumstances.
Putting aside the logic of marrying someone you have only been with for a few days I think even Manilla might find this a stretch.
Why do you not want to spend time together?
Presumably Ireland?
Not sure how many here are familiar with Irish Criminal Law, from a practical perspective the decision will be made at the interview, if a waiver is needed.
The K1 has many disadvantages but not in relation to this.
A 12 year old should be looking at a B2.
Let her parents apply for the visa and yes you will need their permission for you to travel with her without them.