Rent The Deep End of the Ocean (1999)

Beth (Michelle Pfeiffer) is a successful photographer with a young family to support. On a weekend away, she arrives at a hotel for her 15th high school reunion. She looks away for a moment in a crowded lobby, and in those few seconds her three year old son Ben disappears. A frantic police search begins, headed by tenacious detective (Whoopie Goldberg), but it uncovers nothing. Beth doesn't give up, her quest to uncover the truth leads her to a startling discovery...