My recommendation for the best resource is (are you ready? I want to say this gently, and in hope that you will not take this as a personal slight…)
– the best resource for a child is his well-formed father and mother.
Or, how about this. Get two copies of the Catechism of the Catholic Church, one for you and one for your spouse. Map out a schedule for the two of you to work your own adult selves through the entire Catechism (this map will be a long one - the Catechism is long. The Faith is big.).
(1) Parents meet, after privately reading and praying over and pondering the 1st section. Parents discuss the 1st section at an adult level. And after you two adults have discussed the 1st. section of the “curriculum” and determined that you two understand it well, then discuss how you can adapt that section to the level of the child or children.
(2) Then schedule a to-become-regular “Family Faith Time” (or some better name for it), to present and talk about the things in the section with the child or children at their level. You may be surprised at the depth that a child can see into divine mysteries, and in a surprisingly simple way.
(3) Then advance to the next section, and repeat (1) for the next section in the “curriculum”.
(4) Repeat until you finish the Catechism, or your children move out and get married, which ever comes first.
note: the Catechism is an immense resource, with many references that can expand and deepen your grasp of the matters presented. I’d especially urge you to look up every Scriptural reference that is given as you encounter it, and every cross-reference to other Catechism sections that are given, as you encounter them.
note: if you get confused, seek help on anything that becomes a barrier. “This is not rocket science” - it’s even more challenging than rocket science! But God is on our side, in this venture into His revealed Truth for you and your family.