YES, this is a valid interpretation.
The day is clear and bright. The wind is gently tugging at the walkers' skirts. In fact, the way the mother's legs are crossed almost looks as though she is dancing. The sun is shining.
The wide open eyes, the smiles, the round and happy faces communicate a sense of freedom and happiness.
Notice how much yellow is in this picture. Yellow has often been a color associated with joy and light. Red with love and action and in a more negative context: anger or fire.
Vera Williams studied at Black Mountain School for the Arts in North Carolina. Her use of vivid colors has a powerful, emotional impact on readers. Here's a site that offers insight into the psychology of color and how it may relate to an analysis of her designs.
Consider another interpretation