For weeks, the Kurdish-led Syrian Democratic Forces have battled to crush IS fighters holed up in a small riverside hamlet in the village of Baghouz.
Mustafa Bali, a spokesman for the Syrian Democratic Forces, confirmed that the infant died at a camp in north Syria. He didn't provide further details.
Kurdish fighter belonging to the Syrian Democratic Forces (SDF) also died in the attack.
The Syrian Democratic Forces founded in October 2015, has been backed by US-led coalition air strikes, artillery, and special forces advisers.
The US-backed Syrian Democratic Forces said Tuesday they had fully captured the Islamic State group's former Syrian stronghold Raqa, after more than four months of fighting.