For those thinking the Kardashians have been shoehorned into the show, they actually haven't.
Beside's obviously Robert Kardashian's huge involvement during the O.J trial (and O.J living in the Kardashian house right before, were he did indeed threaten suicide in Kim Kardashian's bedroom), O.J, Nicole, Robert, and Kris were the best of friends.
Robert and O.J in particular were best friends for 25 years and were best men at one another's weddings.
Likewise Nicole Brown and Kris Jenner were the best of friends, and the day that Nicole was found dead - she and Kris were supposed to meet up for coffee. In fact Kris knew O.J was a threat to Nicole (as Nicole had secretly confided in her), and Kris has expressed it is her biggest regret in life not doing anything about it.
As for the Kardashian kids, O.J was practically an uncle to them growing up (they called him
"Uncle Juice"), and both families were always going on family vacations together.
Finally as for the Kardashian children being at Nicole's funeral in the television show...well, that's because they really were at the funeral in real life (video footage for the skeptics
https://www.youtube.com/watch?v=W8fTuCCK5U0).