Create a redstone contraption in minecraft

What can we use if pistons or redstone dust are hard to find in the game?

If you don't have regular pistons use sticky pistons (they still push the door block) and if redstone dust is scarce you can run power with redstone torches or place repeaters in the trenches to carry the signal to the piston backs.

The door doesn't open when I press the button — what should I check?

Check that each piston is facing inward toward the door, the redstone dust in both trenches actually connects to the backs of the pistons, and that the repeater is placed facing the correct direction with appropriate delay ticks so power reaches both sides.

How can I adapt this activity for different age groups?

For younger kids, shrink the workspace to a 3x3 area and have an adult place the pistons and trenches while the child places the door block and presses the button, and for older kids expand to a double-wide door, add observers or extra repeaters for advanced timing and testing of different delay ticks.

How can we make the automatic door fancier or more personal after finishing the basic build?

Swap the door block material for a different color, use sticky pistons to create a flush hidden door, replace the button with pressure plates or a lever for different activation, and tweak the repeater delay ticks to change the opening/closing speed.