What is the basis for this assessment? Any kids yourself? You don't know until you have one.
Regarding bias, I never wanted an INTP, I expected a Sensor (statistically likely) and looked forward to somebody different. Being one I knew the difficulties and didn't wish that on my kid. As it was, early upbringing was a disaster, I tried parenting like he was a S (authoritarian, which I understand works with S's from my S friends), just caused him to rebel, to an uncontrollable degree. Just like me as a kid.
I didn't think he was one but couldn't figure it out, it was my wife that clued me in. After a long time watching and thinking I realized she was right. Then, as an experiment, I started to treat him like an INTP to see the results. Like, when telling him that something wasn't allowed, I explained the rational basis for it, and gave him a choice between minor alternatives, instead of saying it's because thats the rules. Other examples ... anyhow he loved it. Eventually tailored his upbringing to one for an INTP, for example he hates sports, especially team ones (barely lasted one half season of kid basketball.) But I got him into swimming, because otherwise if I let him he would never leave the computer and the legos, and the two of us go three times a week. It's perfect, much fewer 'attack of the shadow Fe blowups', and better stability and focus in general. Oh god, yes total lack of any emotional maturity but the brain of a super computer, anyhow ...
As to how you know, you'll find out when you're a parent. Type and personality is largely set in the womb. Sure a lot changes while they grow up, but the basic pattern is written in the genes. His cousin is an ESFP, and you literally could tell in the womb. He was crazy, kicking, moving around, punching. My kid slept all day ...