Well, the effects produced can be manifold! It just so happens that the most convenient route in the life of one Robin Goodfellow is-- usually-- the more soporific applications. Aria especially seems to appreciate it, come bedtime.

(And of course Raspberry had a good few months where she refused to sleep at all without a lullaby. Puck is glad that stage in her development is done with.)

This is not a lullaby, though Havelock may recognize that it has been used as one in the past, and Puck is continuing to hum it more or less into his hair-- perhaps hum isn't quite the word, though it's a tuneful sort of thing.

He had begun a bit tenuously, perhaps unsure as to whether Havelock shouldn't prefer it to be quiet; but when he seems to take it well enough the tune gains a little by way of shape and volume.