If you have Get Together , create a "School Club" and set this specific McLayneSims uniform as the Club Outfit . This ensures all boys in the club automatically change into it when the "school day" (club gathering) starts.

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.

In The Sims 4 , you can use this Basic Kids Uniform to simulate a real school system:

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.