We bought a few things for our kids over the years that were just a passing interest. Basketball, goal, and a jersey. That flame went out about two weeks in. Same with model cars, skateboards come and go, slacklines, telescopes, drones, etc.
If there is any chance that your child is like this, I recommend a pocket microscope. If the fascination endures, then upgrade. The pocket microscopes can be very inexpensive and make good elementary school child birthday gifts.