Taxpayers may be eligible for certain tax benefits if they support or live with their children. Each benefit uses a unique definition of child, partly because the provisions address different tax and social policy goals. Other factors, including piecemeal efforts at tax simplification and complicated family structures, contribute to complexity and increase compliance burdens and noncompliance. A consensus is growing that the definition of child can be simplified without sacrificing important policy goals. Proposals to create a uniform definition of child are similar. The differences between the proposals highlight trade-offs that must be made between simplification and other policy objectives.