The children were travelling on a bus that was hit at a market in Dahyan, in the northern province of Saada.
The health ministry run by the rebel Houthi movement put the death toll at 43, and said 61 people were wounded.
The coalition, which is backing Yemen's government in a war with the Houthis, said its actions were "legitimate".
It insists it never deliberately targets civilians, but human rights groups have accused it of bombing markets, schools, hospitals and residential areas.
Meanwhile the new UN special envoy to Yemen, former British diplomat Martin Griffiths, is planning to invite the warring parties to Geneva in September to discuss a framework for negotiations.