I would advise the book “Jolly, the Ambitious Horse” (hardcover or paperback, that depends on your preferences) to be the starting point for learning algorithms and the control structures in programming: sequences, decisions and loops. By creating the diagram for the story, children get a sense of decomposing problems and representing things through diagrams. All the control structures can be explained and exemplified through different parts of the story. So this can be considered an introduction and an overview. 

However, practice is very important for children to acquire the concepts thoroughly. The aim is children to be able to decompose problems, recognize patterns, abstract them and create algorithms (which, in my children adapted approach, are represented visually through diagrams).

The “Additional illustrations” are a good instrument to expand the story and nourish children’s creativity while practicing the control structures. The point is children to understand this approach (creating a flow diagram) can be applied with any scenario.  These illustrations are also used in the activity books. Children can always use their own drawings instead of the illustrations, however, if you don’t want to change focus and spend time with drawing, these illustrations help expanding the story creatively while keeping focus on the control structures.

Then, I would advise continuing with the activity books to explore the concepts further. “Jolly, the Ambitious Horse - Activity Book 1 - Decisions with logical operators” gets more in depth with one of the control structures - decisions - and introduces the concept of logical operators (which are evaluated in a decision structure).

“Jolly, the Ambitious Horse - Activity Book 2 - Loops. Nested loops. Infinite loops” gets more in depth with other control structure - loops - and introduces the concept of nested and infinite loops. One type of loops, the condition-controlled, use decisions to determine the moment when they should stop, therefore it is important to go through Activity Book 1 before Activity Book 2.