My nephew is 4 and a bit, obsessed with science, engineering, nature etc. He keeps on about stargazing so I’d like to get him a telescope.

I’ve looked at the Celestron range, tried a firstscope, even that seemed a bit much tbh.

So, something he can see some stars, planets and the moon with, and easily so?

Depends on how much you want to spend. A small dobsonian would be OK for a first telescope.

Have a look at first light optics to give you an idea of what you can get for your money.