In his little mind, he clearly was convinced he'd be able to head off to work with Daddy if he wore the proper attire. Careful observation has yielded that it is all about the clothes, his 3 oldest siblings wear school uniforms each day and Daddy wears a suit a tie.
He wanted his twin brother to wear his dress items too and come along, but Declan refused the provided apparel replying "I Stay Home". In the end, playing pretend work and pretend school with Mommy most of the morning seemed to satisfy both. The Tie was optional.