OP if you can manage without going back to work, I'd stay off! I've just finished an 11 month maternity leave, and the children, the husband and the house were a full time job.
Now it's a massive rush every morning and evening and it's not pleasant and I only work school hours ( but I have a commute as well,) it doesn't feel like much of a life compared to the 11 months that preceded.
Plus my DH does not do much and if your DH is the same you may feel hard done to doing a job in the workplace and having to do everything you did before - I sometimes congratulate myself.on getting through the day without murdering my DH!
With 4dcs i would say a nanny is your only option.
The job market has changed a lot in the time you have been off and ex-sahm I know found it very difficult to get a job after their career breaks, you'll probably not be able to command anything like the salary you may have been used to, and childcare for 4 dcs will be huge!
That said if you do want a challenge , why not look to do a part time, school hour, term time job.
If you don't need the money you can afford to plan and wait until you find something that fits in with your life. There are such jobs out there.
Re time off, I'm sure most employers are okay, but many would be unhappy if you took 1 week after another with 4dcs getting ill in succession - but a nanny could cover some illnesses - do your research to see if it's a family friendly employer.
I think you'd be mad to go from sahm to full time, if its not out of necessity! Good luck in any event!