You probably heard before of the "Flynn Effect", the phenomenon first described by James Flynn which states that every new generation has an average IQ higher than the one before and as a consequence, with every new generation, we make new tests that fit the latter.
Now, the above is what the objective facts are and all of what comes after is an explanation of my reasoning and what the implications of the "effect" are according to my own subjective opinion, so you are allowed and encouraged to challenge anything I say below.
What this phenomenon means to me is twofold; First, I think that it's impossible that on average, our children are smarter than us as there is no reason for that to happen and biologically, no species can evolve that fast and the genetic differences between two successive generation is completely negligible. Second, by assuming the first proposition, there is, in my opinion, only one possible explanation for the Flynn Effect and that is that the accelerating dominance and importance of standardized testing in our education system worldwide leads pupils to score higher each time as they become more accustomed to that specific way of testing which leads to obvious conclusion that the IQ test is very far from being completely reliable as it's sole duty is to test how good said person is at taking tests.
There are probably multiple flaws from my logic but however many flaws one can find, this effect will always lead, in my opinion, to the conclusion that the IQ test is not greatly reliable at all.