You will have to be even more organized than the rest of us if you are working with children. Hopefully your 3 year old is one of those 'happy kids' who is not terribly distracting because even the shops that don't forbid kids outright still require your full attention, and unless you have family that can sit for you, the pay is generally not enough to pay a babysitter to go do. When my kids were little I knew that there were certain hours of the day when they were predictably 'safe' to take into stores and I wasn't even doing shops then.
Shops generally have a 'window' of a few days during which they can be performed. Some shops may have restrictive hours or only a specific day when they can be performed. You will need to watch that closely. At 3 or 4 was when my kids started getting sick frequently as they worked their way through everybody's germs from playgroup and nursery school. While it was good for them to build those immunities, it made scheduling anything except doctor's appointments the pits. Luckily most of those illnesses lasted only a day or two, so if you always target performing shops on the very first day of the 'window', a sick kid just lets you do the shop a day or so later while you are still within the 'window' without needing to contact a scheduler to reschedule the work. Schedulers do not want to hear about sick kids or cars that don't start or other things that have come up. They want to get a shopper for the job and move on to other things.
For your first shops I would strongly encourage you to schedule and perform them at a time that hubby or someone can watch the 3 year old, even if kids are allowed on the shop. It will take a handful of shops performed before you get the hang of what is required of you.
So read through the 'sticky' threads above about getting yourself set up and then start signing up with a few companies to see if the shops can work for you.