As a low brass player, I'd say a sousaphone is in the tuba family: the lowest common brass instruments, an octave below trombones and baritones/euphoniums.

A sousaphone in particular is a marching tuba (named after composer John Philip Sousa), constructed to wrap around the player and place the load on the shoulder, with the bell projecting the sound forward instead of up.

Another type of marching tuba is a contra, more common in drum and bugle corps. It looks like a normal concert tuba but with a 90-degree twist to the valves and mouthpiece pipe so that it also rests on the shoulder with the bell facing forward.

Tags for this video have been changed from 'kid, marching, band, sousaphone, marching tuba' to 'kid, marching, band, sousaphone, marching tuba, fanfare, dutch, katwijk' - edited by Eklek

Tags for this video have been changed from 'kid, marching, band, sousaphone' to 'kid, marching, band, sousaphone, marching tuba' - edited by deedub81