Comparing work and SAH-dom (I took a year off on maternity for each of my 2 dcs), looking after small children does not require a lot of brain cells. I have read the full spectrum of parenting and child dev books - that was interesting with dd, but with ds, nothing new. Mn is more interesting now, with anecdotal accounts.
Otherwise, Wheels on the Bus and reading children's books gets a bit wearing.
As for socialising with other mothers, it was pleasant enough but just involved chitchat in each others' houses whilst the children got together and amused themselves. Hardly any cellular activity needed for gossip.
The interesting bits of SAH-dom involved improving my repetoire of homecooked meals, organising the household finances, investments, home inprovements, learning about gardening etc. ie not related to childcare.
As for work, yes, it can be boring. But it can also be as interesting as you want it to be. Depends on the job as well. For me, being in an office gives me sheltered time to devote intense energy and concentration to a project, really crack at a problem. Unfortunately, you don't get that luxury at home. Hence, my brain really does rot somewhat, along with a degree of self-confidence.