Starting with the outline
Most children's first real jigsaw stalls at the same point: a pile of pieces and no idea where to begin. A shaped puzzle solves that. The edge of the finished space scene is a recognisable silhouette, so children pick out the outer pieces first and build inwards. That is the same strategy older puzzlers use, learned without anyone having to explain it.
What the hands and eyes are doing
Each piece has to be picked up, turned and pressed in until it seats. That small push-and-twist builds the finger and thumb strength that later goes into holding a pencil and cutting with scissors. Meanwhile their eyes match colour, shape and picture detail. You will often see a child hold a piece up against the picture before they try it, which tells you they are planning rather than guessing.
Where it fits in the puzzle progression
Forty pieces is the step up from 12 to 24 piece puzzles and the step before the 60 to 100 piece range. It is long enough to need persistence and short enough to finish in one sitting, which helps children stay patient at this age. Finishing the whole picture is a genuine win, and most children want to go again straight away, faster this time. As their skills grow, they move on to bigger piece counts and plain rectangular jigsaws with no outline to lean on.
The puzzle is completely silent, needs no batteries and works indoors on the floor, a table or a tray. The space theme also starts conversations about planets, rockets and stars, so it pairs well with a story or a look at the night sky.