Hi everyone, first post here so please be gentle

I'm a bit stuck with what to do for exercise. I realise this seems like a stupid thing to say, but I haven't exercised in years. I am desperately unfit, I also have arthritis (in my hands but all my joints are VERY stiff).
I have a baby and toddler in tow literally everywhere I go with very little help babysitting-wise so whatever I do needs to be something I can drag them along to.... gym is not an option here! I walk 20-40 minutes 3 or 4 times a week pushing a monstrously heavy buggy, but that's about it.

I'm especially not sure about the sprinting thing - not sure the little ones would be too happy if I sprinted away from them! Does lifting a child count as 'lifting heavy things'?? Help please.