Full-size accordions commonly have 120 bass buttons, but a range of smaller sizes exists specifically to make the instrument physically manageable for smaller players, especially children.
Why size matters more here than for many instruments
An accordion is worn on the body and its weight and width directly affect whether a player can reach both keyboard/buttons and bellows comfortably - unlike, say, a guitar, where a smaller player can still reach a full-size instrument if slightly less comfortably. A too-large accordion for a beginner (especially a child) can genuinely make learning harder rather than just being a comfort issue, and can encourage poor posture or bellows technique that's hard to unlearn later.
Smaller bass-button configurations
Smaller accordions typically reduce the bass side's button count (common smaller counts exist well below the full 120), which reduces both weight and reach, at the cost of some of the full bass range and chord options - a reasonable tradeoff for a beginner or smaller player who isn't yet using the full bass system anyway.
When buying for a child specifically, prioritizing a size that lets them sit or stand with good posture and reach the full bellows range comfortably matters more than maximizing bass-button count from day one - they can move up to a larger instrument later as they grow.
