As you know, I go to a presbyterian church. Many Christians, including my pastor, avoid using the term "in the covenant" when speaking of a newly baptized baby or an unconverted child because it only contributes to the misunderstandings that feed presumptive regeneration. My pastor would say instead that our unsaved children are "in the covenant externally" or "members of the visible church" to avoid this confusion. There can be no unbelievers in the covenant of Grace.
We discussed this previously HERE if you are interested.