The strikes hit four IS-controlled villages in Hasakeh province, the Syrian Observatory for Human Rights said, saying the toll could rise.
The Britain-based monitor said the latest civilian casualties came after two days of civilian deaths in US-led strikes in Hasakeh.
It reported another eight civilians, including one woman, were killed in US-led strikes on another IS-controlled village in the province on Wednesday.
And it said 15 civilians were killed on Tuesday in in strikes on the town of Al-Shadadi.
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The coalition has reportedly stepped up its raids in Hasakeh since the Kurdish-led Syrian Democratic Forces alliance launched a new operation against IS in the southern part of the province on Monday.
The alliance has scored successes against IS in other parts of the province in the past, backed by the coalition which began strikes in Syria in September 2014.
It has rarely acknowledged civilian deaths in its campaign against IS.
In January, it admitted two "likely" civilian deaths last year near the IS stronghold of Raqa, bringing to 16 the total number of civilians the coalition has acknowledged killing in both Syria and neighbouring Iraq.
In total, the campaign has killed more than 4,250 people in Syria, according to the monitor.