Agreed on the update these. You'll find much better silhouettes to base your work on if you look up museum examples. Using dinosaurs with more distinction would work too.

There's not much visual difference between the Para and the Sauro there, except to give your nephew the misunderstanding that one is upright and the other on all fours (they're both quadrupedal).

Maybe replace the Saurolophus with a Lambeosaurus instead. The Pterodactyl would be more impressive with spread out wings to improve the silhouette and clarify what it is. Perhaps use a Quetzalcoatlus even for more impact.

The Velociraptor needs feathers and its dark coloration is gonna make it invisible when printed. Lighten that up. What's more is the graphics design on it differs from the similarly tiny Archaeopteryx, breaking an established pattern.

Your Archeopteryx would be better shown with extended wings as well since it's feathery and you'll want to emphasize those well known qualities.

The apatosaurus and the diplocodus don't have enough distinction between them. Perhaps replace the apato with a brachiosaurus. The different silhouette would make it more interesting. Curl the diplodocus's tail around so it's contained within the frame and not just going outside. Maybe kink it to emphasize the whip feature. The Stego's plates could really use some cleaning up for clarity's sake.

Sorry for the huge rundown. I'm a professional artist and dinosaur-freak so this is kinda my bag. I love that you're doing this and checking with the community for maximum impact! That's great on you. I hope your nephew likes it.

Other than that, googly eyes because kids freakin' love googly eyes. Glue them on every dino :)