If you were to put little notices in people's mailboxes offering them childcare and pet sitting services what are the chances they would actually read it?

I think putting anything on or in mailboxes is against the US Postal regulations. You could try putting them on the front doors of the house instead. I did this once to advertise a service and it actually worked very well. You could knock on the door first and hand it to whoever answers, or just open the screen door enough to place one so the door would hold in place when shut, but make sure a part of it can be seen before the door is open. Hope this helps Debtay374