My 5 yr old fell in love with the Solar System, too! He’s six now and still enjoys learning about it.
I feel blessed to have purchased Apologia’s ‘Exploring Creation with Astronomy’. It is biblically based. No BIG BANG! Yeah! It is read like a story so the child can narrate. We also purchased the Notebooking Journal that can accompany it for deeper learning if you like.
Believe me, we’ve been through many, many secular outer space books and what a relief to find one that is knowledgeable and accurate. ~ Helen