Thanks for these comments Jahmil.
For mother's employment as an exposure, it is very challenging because mother's employment is an indicator for multiple factors (other sources of financial and social support, mother's SES) and also triggers multiple pathways. Most obviously, mother's employment influences both time availability (which you emphasize) but also financial security and the mother's well-being more directly (e.g., is the job physically dangerous, personally gratifying, high-status, flexible, etc)? Each of these pathways may have a different consequence for the child at different ages, e.g., 1 week, 1 month, 1 year, 4 years... Given this, is it possible to be more specific about the exposure? What do you think is potentially aversive about mother's employment? Lack of time w/ a primary caregiver? Primary caregiver's exhaustion, anxiety? And what are the key confounders and effect modifiers (you mention SES - completely agree with that one) you would need to measure to describe this correctly? This is why studying social determinants is often so much harder than studying clinical exposures - social exposure have so many consequences and also so many antecedents, it is difficult to isolate effects. Natural experiments/policy differences might be appealing here. You might for example be able to look at natural experiments such as the welfare reform in the 1990s, which I believe had some level of state to state variability in the work requirements for mothers.
-Maria