Synonyms of waif
foundlingA foundling is a baby that has been abandoned by its parents, often in a public place, and that has then been found by someone.
strayStray is also a noun.
• The dog was a stray which had been adopted.
urchin (old-fashioned)An urchin is a young child who is dirty and poorly dressed.
• We were in the bazaar with all the little urchins watching us.
Thesaurus for waif from the Collins English Thesaurus