Operating agencies shall serve eligible migratory children—according to their needs—in the following order:

(1) School-aged currently migratory children.

(2) School-aged formerly migratory children.

(3) Preschool currently migratory children.

(4) Preschool formerly migratory children.

(5) Provided, That if in order to provide Chapter 1 Migrant instructional services to school-aged currently migratory children, it would be necessary to provide day care or similar services to preschool-aged currently migratory children, and no other funds—other than Chapter 1 Migrant funds—are available for that purpose, or an operating agency may provide Chapter 1 Migrant instructional services instead of day care services to those preschool children as if those children had a priority higher than school-age formerly migratory children.