。
She smiled at the baby.
Literal
She [topic-は] baby [to-に] smiled-toward.
微笑みかけた uses the compound verb pattern ~かける, where かける adds a directional sense — the smile is 'aimed at' or 'directed toward' the baby. 微笑む (ほほえむ) means 'to smile softly,' and adding ~かける makes the action targeted. This productive suffix appears with many verbs: 話しかける ('to address, to speak to'), 呼びかける ('to call out to').