Funny that the SSCPO topic should crop up.
I just finished a little surface mount version of Dave's circuit.
Decreasing the value of the resistors in series with the speaker and it performs quite nicely on 3 V from a pair of AA cells. Adequate volume, but not loud enough to annoy parents........ important because.....

It's tucked into a key I 3-D printed for my grand daughter Tessa, who just turned 3 this week. You might recall a photo I posted a few weeks back of her trying her hand at the Brown Bothers paddles on my K2. Now she can have a key of her own.

A roller-lever microswitch is hidden under the trunion, and there's provision to bring out a connection to actually key a tranmitter .... one day....

Photos are attached.

73
Jim, N5IB