Dave Bonta's short poem is about the gap between how children make art and how adults do. The first stanza says that children's art "sings," and then adds a quiet loss: "we all unlearn to limn." To limn is to draw or paint, so the idea is that growing up trains the natural, joyful ability out of us rather than building it in.
The second stanza turns to the source of that singing. "Beginning eyes" are fresh eyes, ones still new to the world, and they "take great light." There's a nice double sense here: they take in plenty of light, and they take it greedily, without hesitation or self-doubt.
The speaker sounds wistful, a little rueful, but not bitter. There's admiration for children and a gentle sense of something misplaced along the way. The mood is hushed and bright at once. With so few words, the poem leaves room for us to think about our own childhood drawings and what we might still recover from them.