In this scenario, the nurse should take the action of obtaining the child's dietary history first. By gathering information about the toddler's current dietary intake, the nurse can assess the specific problems and challenges the child may be facing.

This information will be crucial in developing an appropriate plan of care to address the poor dietary intake. Once the nurse has a clear understanding of the child's dietary habits, they can then proceed with other actions such as encouraging the family to be present during mealtimes, offering nutritious snacks, and providing instructions on praising the child when they eat.

However, obtaining the dietary history will provide essential information for the nurse to make informed decisions and interventions.