Not trying to be a purist or a snoot here, but even a 2 year old being ear-trained, whether it is on an instrument in tune, or out of tune. You know how their little minds are like sponges? It turns out, their ears are as well.
And that can last on into adulthood. My husband, who was never musical, never sang, and listened to the radio, couldn't match pitch. Now that he has been playing ukulele and getting close to the chords and strings and sounds, his pitch is improving. I have been amazed.