Planning to start ghar ka milk for my kids, are tetra packs better or packet cows milk? Pls suggest

I wonder why everyone is suggesting tetra packs! I mean, I understand that in todays' times you cannot trust purity of anything that is sold in market but everything that is packaged means that is being processed and must be having some preservatives that would keep it good for the said time. And if so, why do you want to give your kid anything that has preservatives and especially milk. You can buy milk from designated Mother Diaries. Also, there are simple tests at home which you can do to check whether the milk is adulterated or not. Check this link below and can follow it in daily life. http://indiatoday.intoday.in/story/simple-home-tests-to-check-adulterated-milk/1/198595.html