Life plan musings

I keep thinking on and off about what to do with my life, I'm sure it's a cycle thing because for a large chunk of the month I'm perfectly happy.
I'm 30 very, very soon and that to me seems like a pinnacle age, when my Hubby turned 30 (8 years ago, had to get that dig in) we had only just got together and he was distraught at the prospect of leaving his 20s. However he was already successful in his career by then, had risen to top management and although the last 3 years has seen him soar he put that groundwork in during his 20s.
I never really knew what I wanted to do work wise, my parents would say I was the last person they would expect to have had kids and be a SAHM, they thought I would be career focused. I did my degree in History & Media, got a good 2:1, thought I would end up in marketing like all my Uni friends, but I got a job in retail to tide me over until I found a 'proper job', met Hubby, who was my boss and moved with him to London (from Leeds) after about 3 months so that he could work at the Head Office. I fell pregnant almost straight away and so I never got that 'proper job'. I did some temping for a charity whilst pregnant which I enjoyed and then we moved from to the suburbs and had more children. Still no 'proper job' unless you count Little Milestones, which a lot of people, including my parents, didn't.
My friend and I started Little Milestones (online retail) and ran it for over 3 years before we sold it. We worked very hard in that time, the business took off, we had to get an office and a member of staff and everything. In that time we each had another child and in the end I think we just lost the enthusiasm, we were at a crossroads where if we wanted to take it further we had to invest more time and money that neither of us had. Then my friend's hubby got a job in the States and I didn't want to carry it on on my own, nor work with someone new so we sold it.
That was almost a year ago. My friend has still not made it to the States and I still don't have a 'proper job'.
That said, I'm very lucky in that I don't need to work, infact the Childcare wouldn't make it worth my while, but that doesn't stop me pondering on what I should do with my life. I've been out of the work place, if I was actually in it at all, for a long time, coupled with the fact that working for someone else after running your own business would be hard in itself. Adding to that the fact that for the most part I love being at home, having the time to do stuff I like, being there for the kids. But I can't shake the feeling that I need to be challenged more, although what can be more challenging than 7 year old girl thinking she's 15, a 6 year old boy with an attitude to match the length of his gangly legs and a 2 year old tantruming little girl who seems to have one medical drama after another!
No doubt I'll muse away for a wee while yet on this before I actually do anything about all my musings, so there may be more musings on my non-life plan to come...