There are not many beginner-friendly apps that I am aware of. However, there are a few websites you can use.
BugGuide has a relatively nice picture-based search system. You will also gradually learn to easily identify various characteristics of an insect, thus making your search easier.
Insect identification is more beginner-friendly and more suitable to your kids.
You can also ask either here, or perhaps in the reddit community if you have trouble identifying a particular bug.
If they become interested I would recommend searching your local book store or library for a good field guide (depending on your location). Entomology can be a fun excuse to get out of your house and learn something in the process.