I am assuming you have name changed from the opening post to the later ones.
It is all well and good people suggesting volunteering but with children aged 9 and 6 you still need to be available for them for the school holidays so volunteering in a school is a good idea rather than a shop that you wouldn't be available for 13 weeks of the year.
I have been a long term SAHM for 18 years and I do volunteer. I am certainly not bored. I only have one other friend who is also a long term SAHM everyone else did return to work but now juggles childcare and holiday clubs and swapping play dates with other parents who also struggle to afford the summer holiday stretches.
What do people at the school gates talk about? Just their jobs? Things they watched? Their children? I never had any problems talking to people for the 10 years I was in the primary school playground for.
Stop apologising for being a SAHM, some people think your choices are a judgement on their choices. My sister worked full time with 2 children, I never judged her, she never judged me. We both know that we chose these different paths, it does not pit us against each other. People parent differently. Each family makes choices on what works best for them. I absolutely love being a SAHM.
Of course you can go on a walk with no destination, you just enjoy the walk. Why wouldn't you go to a cafe? I think you are over analysing everything. Being a SAHM isn't for everyone as the comments on here demonstrate. But this isn't the 1980s with 3 tv channels. Even at home there is the internet, podcasts, audiobooks so you can be doing housework whilst listening to interesting things. On walks you could also listen. Stop being so hard on yourself, enjoy the freedom you get to experience.