To examine associations of household crop diversity with school-aged child dietary diversity in Vietnam and Ethiopia and mechanisms underlying these associations.

We created a child diet diversity score (DDS) using data on seven food groups consumed in the last 24 h. Generalised estimating equations were used to model associations of household-level crop diversity, measured as a count of crop species richness (CSR) and of plant crop nutritional functional richness (CNFR), with DDS. We examined effect modification by household wealth and subsistence orientation, and mediation by the farm’s market orientation.

Two survey years of longitudinal data from the Young Lives cohort.

Children (aged 5 years in 2006 and 8 years in 2009) from rural farming households in Ethiopia (n 1012) and Vietnam (n 1083).

There was a small, positive association between household CNFR and DDS in Ethiopia (CNFR–DDS, β = 0·13; (95 % CI 0·07, 0·19)), but not in Vietnam. Associations of crop diversity and child diet diversity were strongest among poor households in Ethiopia and among subsistence-oriented households in Vietnam. Agricultural earnings positively mediated the crop diversity–diet diversity association in Ethiopia.

Children from households that are poorer and those that rely more on their own agricultural production for food may benefit most from increased crop diversity.