I understand how you feel OP. I have been a SAHM since my first child was born 10 years ago. None of our families live in the UK, so it is just us.
When my younger one finally setted in school, I considered going back to work, but if I want to work in a professional job like I had before, it requires me to work full time without much flexibility. If I choose to work a more casual / flexible part time job then the additional income seems very petty compared with what we have already.
My husband and I discussed about this together. Working part time with a bit more money doesnt seem to be worth it for us. Hubby has a good salary, we are comfortable with one income. Just to make it clear as a lot of people on MN seem to have problems with SAHMs getting benefits, we have never qualified for any sort of benefits including child benefits from day 1. In fact he pays more taxes with only one salary than same amount as combined income.
Right now, I can do all the school runs. I can take them to afterschool sports and music lessons. I also spend time making sure they do a bit language learning (we are not British) and instrument practise everyday. We can choose to have a family holiday (specially going abroad to see grandparents from both sides) rather than spliting annual leaves to fit school holidays around. If I were to start a full time job all those wouldnt be possible.
During week days I do all the shopping and laundry, cleaning and meal preparation. I also cook lunch everyday for hubby because he is working from home full time. I usually get a bit rest after lunch. I can sit down and have a cup of coffee and read a book, this is pretty much my only free time. Once the kids are out of school, I will be busy until they are in bed. Occasionally I could catch up with a friend in the morning for a coffee or lunch, but this is really a once a month thing rather than the usual.
Of course I dont have to send them to extra lessons and I dont have to cook lunch everyday, but for us it is a personal choice and an agreement we are both happy with. Hubby really appreciates what I do and knows he wouldnt have progressed his career as much if I wasnt there to take care of the rest. We have a happy and solid marriage too. As for pension, hubby has both state and private pensions. We own a house abroad and are in the process to buy another house here. By the time he retires, we would have extra rental income to top up. We also have life insurance if anything happens to him I will get a big lum sum payment.
I think before you decide to become a SAHM you need to plan for it. If its something you are both happy with and can afford to do so, I dont see any reason why not.Good luck!