Wookies have an average lifespan of around 400 years, so the child-to-adult ratio will of course be lower. Litter births are still possible, they just would happen not very often. Because of the sudden load of 6 or more children (say once a decade), it is also likely that the Wookies practice more communal child-rearing than the human nuclear family model, leading to children the same age being dispersed widely (perhaps across the planet).
This also helps with genetic diversity, since wookies growing up locally with similar ages are less likely to be related.
Wookies have an average lifespan of around 400 years, so the child-to-adult ratio will of course be lower. Litter births are still possible, they just would happen not very often. Because of the sudden load of 6 or more children (say once a decade), it is also likely that the Wookies practice more communal child-rearing than the human nuclear family model, leading to children the same age being dispersed widely (perhaps across the planet). This also helps with genetic diversity, since wookies growing up locally with similar ages are less likely to be related.