There is plenty of evidence that maternal leave is beneficial for children. Go to Google Scholar and search "maternal leave child outcomes".
A sampling from one paper:
>We find considerable associations between early returns to work and many of the outcome measures [regular medical checkups and breastfeeding in the first year of life, the receipt of all DPT (diptheria, pertussis, and tetanus)/Oral Polio immunisations (in approximately the first 18 months of life) and cognitive and behavioural assessment scores at age 3 or 4]
A sampling from one paper:
>We find considerable associations between early returns to work and many of the outcome measures [regular medical checkups and breastfeeding in the first year of life, the receipt of all DPT (diptheria, pertussis, and tetanus)/Oral Polio immunisations (in approximately the first 18 months of life) and cognitive and behavioural assessment scores at age 3 or 4]
http://onlinelibrary.wiley.com/doi/10.1111/j.0013-0133.2005....