Today my younger daughter - the beautiful singer - arrived at home and I had a long chat with her about this theme. She is studying at a musical college for singing, piano and organ, and music teacher.
She started with early musical instruction in the kindergarten. At first they learned rhythm with Orff's instruments, and she puts special stress on rhythm as the basic of all music.
Five years of age she started with the treble recorder. She recommends it warmly because it is easy to play and easy to carry. The child has his own instrument, and when blowing in you get definitely and immediately a tone out. (Not always the case with the trumpet family or reed onstruments, ore a fretless string instrument.)
In her opinion you can't put a kid of the age Peter is talking about to choose his instrument out of a room full of such. When trying them a child would choose the recorder at last because of all this above.
At first it might be a plastic recorder (there are some really good ones), she says, or a wooden one with a plasic mouthpiece because the youngsters tend to bite and spit a lot at first. Later on they might be handed over a real wooden recorder.
It was also fun for her to play together with other kids, playing different parts. And - before she could read a book she could read sheet music.
I hope these experiences of a professional will be of some help to you.

I wish you a Merry Christmas
And a Happy New Year

Wilfried