While I understand your concern for your teen’s online safety, I need to clarify that secretly tracking someone’s Instagram activity, including likes, without their knowledge is not possible through legitimate means. Instagram’s privacy settings and API restrictions prevent this. The only way to see someone’s likes is by having access to their account directly (which you mentioned you’d prefer not to do) or if their account is public and you manually check each post they’ve liked—which is very impractical.
A better approach would be to have an open conversation with your teen about online safety. If you believe monitoring is necessary, consider using established parental control apps that work transparently with the child’s knowledge, fostering trust rather than secrecy.