Hadith.429 - Abu al-Numeir, the freed slave of al-Harith ibn al-Mughira, asked Imam Al-Sadiq عليه السلام: "Tell me about the age up to which a child can be washed by women." The
Imam عليه السلام replied: "Up to three years old."
Our Shaykh Muhammad ibn Al-Hasan mentioned in his book, ‘Al Jamiah’, a girl who dies among men during travel. If She is older than five or six years, She should be buried without washing.
If She is younger than five years, She can be washed.
He mentioned a related narration from Al-Halabi attributed to Imam Al-Sadiq.