No sensible parent falls out with a free babysitter.

While there are many valid reasons to stop using somebody as a childcare option, if a trustworthy adult is willing to watch your kids for no money, that is not an arrangement that you want to screw up. If that person happens to be a family member, even better—they should have more of a vested interest in your kid than a random babysitter who may not come cheap. This kind of arrangement is not a privilege that everybody gets.

At the same time, there are plenty of people whose relatives have young children who feel like they are taken for granted and mistreated when they agree to babysit for them. Many parents take this as an excuse to act out in ways they might not with a professional. It can also make them far more entitled to their time, and expect them to watch their kids even when it is inconvenient, or puts too much strain on their family members. It is not uncommon for arguments to occur because of a difference in expectations between parents and their relatives about how much childcare they are going to participate in.