TV helps. My mom was single mom and poor and and worked hard every day. But I was alone. I felt abandoned.
Make your kids feel more love and fulfill thier basic needs and talking about any topic will be fine. It's good to teach them so they are aware of the world surrounding them

At 12 I understood what was rape. Death too. Thanks to watching tv, I saw a movie where a girl was getting raped. That almost happened to me. A close relative sat down next to me and was asking for sex and more and I said, I'm gonna tell my mom and he stopped.

I'm glad I moved to this country, away from horror. He'll is here in real life, there's no heaven. Only for pets

Around 3-4. At around 5 my son developed a fear (had nightmares I was dying). The best thing I read was to be clear/not make false promises — I was young and healthy, it would be very rare for a young, healthy person to die, I expect to live to be old, etc. The worries passed. My other children did not go through this fear period.

Age 3, DS grandfather passed away and we told him. Not sure what he understood per se, but he had followup questions. Sesame Street website (recommended to me by a friend) had surprisingly good resources.

3.5 is old enough to understand death, but a young child will understand it differently than an older child or an adult.

There are so many wonderful books on this topic. Try Amazon or ask at the library. There's at least one for every faith tradition.