Hey, if you ever find a comforting secular answer for fear of death, I'd love to hear it; it'd probably do wonders for my anxiety.
For context, I was raised Catholic, but from my recollection, I never really believed in it. My family eventually stopped going after all us kids went through confirmation (also when I quit CCD). I think they only really went at all because they thought it was important that we were raised with some sort of religion (for reasons that I don't understand). I think the formal nature of a lot of Catholic rituals really helped push me away from a religious point of view.
If I were raising a kid, I'd definitely lean into the existential uncertainty. I think if I had been introduced to the existential uncertainty at a younger age, I'd probably be more comfortable with it now. That said, I think it's still important to introduce children to religion fairly early on as well, in a context of just "this is something that exists in the world". Because no matter what, somebody will try to get them to convert at some point.
Also, I think you're probably right to be concerned about everyone trying to "save your souls", given the deep evangelical streak in most modern Christianity. It wasn't so much a thing in the church I grew up in, but my husband was sent out "soul winning" every weekend for a while.
That said, I think the closest thing to what you're looking for might be Unitarian Universalism. It came from some pretty radical sects of Christianity (by that I mean super-duper heretical from my Catholic upbringing), but it has evolved into a sort of anything goes, no specific religious dogma. As I understand it, most UU churches don't even have a stated belief on the existence of God at all. I've never sought out that sort of quasi-religious community, so I can't say for sure what it's like; my only experience with the UU church has been through my incidental experience living near one (when I lived nearby they ran a nice cafe to raise money for various social causes, and they made a pretty good soy chai).