# **C Data**

The data used in estimation were extracted from the US Early Childhood Longitudinal Study birth cohort (ECLS-B). This study follows from birth through kindergarten a nationally representative sample of children born in 2001. The data were collected over several waves to capture child development. We focus on the second wave, collected between January and December 2003, when the children were two years old.

## **C.1 Estimation Sample**

As mentioned in Section 3, we arrive at our estimation sample by imposing three main restrictions: we focus on two-parent and one-parent households with only one child, who is two years old; we restrict one-parent household to cases where the parent is the mother; we focus on households in which the father, if present, works full time. In addition, we impose other restrictions that are less costly in terms of observations lost. We drop households where parents’ main jobs include shift work; we eliminate households using non-relative or relative caregivers that take care of multiple children at the same time; we drop two-parent households where both parents work full-time but do not use outside child care; we drop single-mother households where the mother works full- or part-time but does not use outside child care; and we trim the top and bottom 0.5 percent of hourly earnings conditional on gender and education.

In Table C.1 we report how the main restrictions affect our estimation sample as they are progressively applied to two-parent and single-mother households, respectively. Per the first restriction (fourth and fifth columns), we keep households with three or two members– mother, father (if married), and a two-year old child. We do not drop households that go on to have more children after our sample period but drop households in which the two-year old child already has other siblings (biologically or through adoption) during our sample period, or that include additional adults.

Per the second restriction (sixth and seventh columns), from the previous set we select the households where the father works full-time. Full-time is defined as working for pay for no less than 40 hours a week. We eliminate all households where at least one parent does shift work, since shift workers have distinct child care needs. We eliminate a few (eight) observations for which child care use seems measured with error, as both parents work full time (not from home) yet do not use outside child care.

Per the third restriction (fourth column), from the previous set we focus on parents that use either exclusive parental care or a combination of parental care and either relative care, paid non-relative care, or paid center-based care. Note that all parents in the data provide at least some parental care.

The estimation sample is composed of households that are, on average, more educated than those in the full dataset. Among married couples, wages are somewhat higher for mothers in the estimation sample than the full dataset while their participation rates and father’s wages look fairly similar. For single mothers, participation rates are higher in our sample but wages are about the same. Child’s cognitive score is also higher in the married-household sample than the full dataset but is practically the same for single-mother households.

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