Never too young for a computer.
Just keep the smartphones and crap away.
Not all computers are bad for children's brains
Discussion
What do you mean? What kind is healthy for them at young age?
I would say one that has no way to connect to the Internet and let you play with code/programming, with no apps. First time I think about it though...
So old school GameBoy?
I was rather thinking of some pack including things like a raspberry pi, a keyboard, a screen, connections and "real world" interfaces : sensors, motors...
Which would make it possible to engineer basic and playful uses (like : water the plant when humidity is that low, switch on this light when I clap, or whatever safe thing the child is interested in). Learning while playing with tangible things.
A friend of mine had his room full of tiny self-designed robots when he was a kid. He won children engineering contests and is now an engineer. He had a lot of fun doing this.