Use the Fashion Authority Mod to assign this outfit as a situational requirement for school lots, forcing all child Sims to wear it when they arrive.
If you want it to be their official school outfit, use the MC Command Center mod or the cheat sims.modify_career_outfit_in_cas to manually set this CC as their career/school wear. Key Details of the Item Category: Sims 4 / Clothing / Male / Child / Everyday. Compatibility: Base Game Compatible. BASIC KIDS UNIFORM BOYS BY MCLAYNESIMS AT TSR B...
Often includes a clean, preppy look such as white shirts, trousers, or blazers with ties. Basic Kids Uniform Boys - The Sims Resource Use the Fashion Authority Mod to assign this