Gilbert Cocteau and Serge Battour from 4th volume's cover of the manga "Kaze to Ki no Uta" or "The Song of the Wind and the Trees" (1976-1984) by Keiko Takemiya
If Pinestar was the Mi of his kits, why didn’t he try to take any of them with him when he left? Like Brightsky keeping some of her litter. He knew how the clans were, he was specifically leaving to get away from it, why did he choose to leave his children behind?
It wasn't a choice. Brightsky gave birth in the home she bolted to; Pinestar wasn't going to be allowed to take his children unless he snuck out with them.
He wishes he did something, when he sees what became of his son. But he tried to be brave when he left, announcing that he would not be coming back, and where he would be going.
He thought that was the right thing to do. Unfortunately, no one else appreciated it the way he hoped they would.
If he DID though, ThunderClan would not have allowed that. They see it as kidnapping. Being Mi doesn't mean you're allowed to do literally anything you want, especially if you do have a Ba involved.
In cases of handoffs (surrogacy, secret halfclan kits being given to their other parent, etc) it's actually SUPER important you do it before 1 moon, so you can pass the disappearance off as a fading kit. There are no funerals thrown for fading kits besides the Mi and any Ba quietly burying the body, so this is the time where you smuggle the baby out.
So you need all the Ba on board with such a handoff, in addition. Cloudtail is an example of that actually! When Brightheart surrogates, he is fully aware of how many are ACTUALLY faders and who is receiving their child.
Tigerkit was like 3-ish moons when Pinestar hit da bricks, unfortunately there wasn't a way he could take him along... plus it wouldn't quite make sense with how he was having nightmares about murdering his son.