The main research question is how the number of kids affect mothers’ labor force participation and working hours. The labor force participation is a binary variable, so you will need to use the probit model. Don’t forget to calculate the marginal effects to correctly interpret the effects. Working hours is a continuous variable, so you may use a linear regression. In addition to the number of kids, include more control variables such as mother’s age, mother’s age at the first birth, mother’s race dummies, mother’s education dummies.