Ok, here is my 2 cents. . .
I am a SAHM with 6 kids - ages 15, 13, 12, 8, 19 months, and 2 months. I have also been trying to supplement my husbands income by selling on various sites. I have been quite successful as of late so that requires more of my time.
I try to do things mostly at night when the kids are in bed but if the youngest 2 happen to nap at the same time (doesn't happen very often) then I also do as much as I can then. I also sometimes have my oldest 2 kids watch the babies for an hour or 2 after school and then compensate them with either a small amount of spending money or by buying them something small that they have been wanting.
It is hard to balance an at home job and young children but you just have to do the best job that you can and remember what your priorities are. Also best to try to stay calm and not get too stressed out if things aren't going as smoothly as you would like. Remember, the work will still be there later if you don't finish it but your kids will only be this age 1 time...
If my 19 month old wakes up from her nap while I am in the middle of packing up items to ship and printing shipping labels, I have her help me. She puts all of the packages in a basket for me and hands me boxes and such. She loves it and it lets me finish what I am doing before the baby wakes up!
HTH!