Is there a way to limit volume with a parental passcode on android? I know there are apps for limiting volume, but is there any way to secure those limits so a child cannot change them?
If you are on a tablet running recent version of Android OS (4.3 and above), you can create a restricted user profile for your child. There you can simply disable access to the app which you used to limit the volume.
For older versions of Android OS on tablets and on phones (restricted profiles are disabled for phones even on latest Android OS versions,) you can try various "app protector" type of apps, that provide password-based mechanisms for restricting access to various installed apps.
If you have Tasker, you could create a task that detects when the volume is changed. If it goes higher than X, it will run a task to reduce the volume back to X.
Tasker also lets you password protect groups of events, and you can enable Tasker to be an Administrator on the device.
Your child would be able to breifly set the volume higher, but it would always reduce back down. They couldn't disable the tasker event without the passcode, and they couldn't uninstall or disable Tasker since it is a device admin.
Of course, they could always get around it somehow, such as clearing the data on the app or figuring out how to remove the Administrator flag so that Tasker could be removed. It is a cat and mouse game. But this solution should suffice for people who aren't as technically minded.
Kind of late, but I found one I really liked: Max Volume Control. It allows you to lock the controls and starts up when you restart the device. So far my kid hasn't been able to circumvent it.