I'll need to provide a magnified view, but the Motion Greeting Card has a stiff foam core, with thick paper glued to the foam core, as front and back faces.
Imbedded into the core, is a plastic square frame, for mounting the pivoting pendulum.
I didn't realize, but by putting the coil portion of the back and forth lever, the whole moving portion is then very light...oscillating gently at about 2 hz, or two times per second pendulum.
Flat magnets are stuck to card, in front of the oscillating coils,...and likely the coil is simply with the two fine wires, loosely, thus avoiding needing a brush or commutator.
The circuit is, simply powered directly from solar cell, (no battery), plus there is a small,
47 ufd. type power input cap.
And a small epoxy dab over some circuit, no switching or loudspeaker output.
Just the two pwr wires coming in, and two wires to drive the coil for oscillating lever.
A project box, could start with just those (4), connections, via. some regular banana jacks.
Then add things from there, to make it interesting to, say, an 8 year old.
(Hopefully old enough to not be swallowing things, small parts or batteries!).