Omg! You already have two kids, a boy and a girl - and theyre still pestering u?! depends on how open ur relationship is - but maybe joke with them and say 'why dont u have them instead?' or be serious and tell them 'whose going to provide for them?' or be blunt and say 'both wifey and i are happy with the two so leave us alone'.
Just say k Allah swt ka shukar hai k us nay hamain dono namatain dein, bus ap dua karain k hum in dono ki sahi perparish ker sakain. If you are close to your mom or dad tell him/her how it bothers you.
This reminds me of something on Sara's wedding card given to her by guppies that said "Allah Karay, Allah Kare, Allah Kare....Jo bhee kare ga Allah hee kare ga, hum ne kya karna hay" or something along those lines.
Sara, congrats on your marriage by the way. Great couple!