Kion wasn't born during the film. He's only from The Lion Guard which is not canon to the films. He's only from the spin-off from to film. Kiara is the only child in the films while Kion is from the TV series.
I'm interested in finding out how old Kiara is in The Lion Guard, as that'll give us some indication!
It makes sense that he'd have been born after the events of Simba's Pride, but considering the film cuts out a portion of Kiara's childhood and then shows her to be pretty much fully grown, Kion could be born during that time. So by the time The Lion Guard takes place (considering he's got a bit of a mane, I'm guessing he's not a very young cub) it could be set after Simba's Pride.
If this is the case, Kion's absence in the second half of Simba's Pride could be explained:
1. He's very young and his parents don't want to bother him with everything else going on (e.g. Kiara falling for an outlander, Kovu being invited to live with them, then Kovu being exiled) so Kion is always being left off-screen with babysitters.
2. He has already begun his training for the "lion guard" and is busy with that throughout the film. So busy that he manages to stay off screen the whole time! (if this is the case, Kiara could be an adolescent/young teenager in The Lion Guard!)
I'm expecting him to be born after the events of Simba's Pride, but I think there are okay-ish explanations available if he were to have actually been born part way through the film.
Well...he didn't make any appearance on Simba's Pride, so I thought he was born after Kovu became Kiara's mate, but then again if you look into the Character list of The Lion Guard ( link) ) You can't find Kovu names at it, so maybe he was born some-time during Simba's Pride, grow up and sent out to guard the prideland ?
He was born during the beginning of lion king 2 simba's pride.
Because Kiara didn't want to be queen. But I lion guard she seems to be a preteen. She seems to have matured and aceppted her role as Queen. " At least I now what I'm going to be when I grow up. What about you little brother? " Plus Nala was pregnant or Kion was an infant. During that time. I say it adds up.
I think he was probably born after the lion king 2 but nala was problably pregnant with kion when kiara was out looking for kovu or in the ending where they all roar together. Of course its sad to see that kovu is not in the lion guard yet, but hopefully disney puts kovu in the new show. I'm pretty sure lots of fans will love it.
Kion was born when her sister was in her teen years Kion the 2nd child of Simba and Nala left and started his own pride so it means he was born after Simba's Pride and left early in a young age and continued the lion guard
I think Kion was born 1 year after Kiara was born. There is an episode of the Lion Guard titled "The Morning Report" where we see Kion and Bunga (aged about 4 years old) in the crocodile territory. That must have been at the same time Kiara met Kovu.
He appears to be the exact same size and age as Kiara so it makes most sense to me that he was born a few seconds or minutes after Kiara. Therefor he was born before the events of Simba's Pride just like Kiara.