I need to update Roblox my kids say to me

In the European Union and Japan can you actually delete the App Store app. Have a look at this support article about how to ‘Delete certain built-in apps from your iPhone or iPad in certain countries or regions’ —> Delete certain built-in apps from your iPhone or iPad in certain countries or regions - Apple Support To redownload the App Store app go to Settings, then tap Apps. Tap App Installation, then choose Restore App Store at the bottom of the page. You might also see an option to reinstall the App Store when you tap any links to apps that can be downloaded from the App Store.

In many countries certain built-in apps cannot be deleted, in which case read this support article --> Download apps on your iPhone or iPad - Apple Support

The App Store app is somewhere on the device. It can be hidden* by you, or by an administrator if the device is managed by an education or business institution. In the latter case you need to contact the administrator.

Here are other possibilities:

See if it was hidden with restrictions:

Screen Time - Allowed apps Set up parental controls to manage your child's iPhone or iPad - Apple Support

- "If you turn off an app or feature, it won’t delete it, it’s just temporarily hidden from your Home screen."

- Settings > Screen Time > Content & Privacy Restrictions > [Enter passcode] > Allowed Apps

- Settings > Screen Time, scroll down, then turn off "Share across Devices"

See if it is in the App Library -->

Organize the Home Screen and App Library on your iPhone [iOS14] - Organize the Home Screen and App Library on your iPhone - Apple Support

"Search for it ( Use Spotlight Search on your iPhone, iPad, or iPod touch - Apple Support ). Swipe down from the middle of any home screen and type the name of the app into the search field at the top of the screen. If it is in a folder, it will show the folder on the right of the app name after you tap on the app when it appears in the search."

"Reset the Home screen layout which will return the [app] to the home screen as long as it isn’t restricted. When you do this, it returns the home screen to out of the box condition and it will destroy any folders you had on the home screen. Settings > General > Reset > Reset Home screen layout."

* Set up parental controls to manage your child's iPhone or iPad - Apple Support "If you turn off an app or feature, the app or feature won't be deleted, it's just temporarily hidden from your Home Screen."