I play classical music during art lessons and am having trouble finding cheerful pieces which have an even mood throughout with no surprising volume changes. Any suggestions please?
After a minor detour to suggest Mozart clarinet quintet (perhaps) I thought you might consider instrumental music with instruments noted for their lack of dynamics, eg harpsichord, lute (& by extension much guitar music) which admittedly narrows your musical eras a bit. Or recorder ensembles.
Also the Brandenburg Concertos (if I remember correctly) don't go in for extreme dynamics or shifts of tempi.