Typically tracking devices is something that we don't talk about because of breach of privacy, however since the question was phrased as a juvenile to parent relationship it might be somewhat permissible.
In the meantime, no. There's no way to "sneak" an app or anything else onto a device. There are several apps or services that can be installed or used on devices by the device owner (usually the parent). Verizon has Smart Family, Google has Family Link and there are a ton of others on the Play Store. Which one is right for you? Well that depends on what the purpose is, what information is desired and device compatibility. For example Verizon's offering will tell you what apps are being used, can track location, send alerts based on location, the hours of use and has some parental controls and limits but is only compatible with some devices. Then it also has a subscription fee and the app must be installed on both devices to get all of the functions. Without installing on the child device you can get alerts about texting and some limited use information but not much else. Kind of the same with Google's offering. So neither would be able to tell you the device location without a full install on both devices.
Don't get taken. There are a lot of ads for tracking software and monitoring software online that claim to offer these features and some without installing on the other person's device. Most of these are false claims and some will tell you one thing then instruct you to do another. It's shady at best and malicious at worst. Stick with reputable sources, names that you know and trust and most of all do your due diligence by checking reviews from multiple sources as well as finding out what the limitations are so that you're not disappointed. This is because most of these services cost or require subscriptions.