Mine are 6 and 3, so the same age gap as you OP but we're one year on.
When they were 4 and 1, I made a spreadsheet of all the really good parks within about an hours drive. I found that there were several that included lots of different bits e.g. a bike track (does your 2yo have a balance bike/scooter?), a decent playground with sandpit (essential - mine will spend a good 40 mins in the sand!), a wooded area for playing with sticks, a cafe, toilets, some water for paddling/feeding the ducks, etc.
So a typical Saturday for us looks like 40-60 minutes of TV for the kids in the morning while I have a coffee and pack a bag for the day (include snacks and some robust monster trucks or a remote control car or something). We potter around the house for a while, look at books, they play together and sometimes I join in / intervene in a squabble, then around 9 we set off, get to the park around 9.30 or 10. Because the parks have so many different areas, we can usually kill several hours there. Yeah, its not wildly exciting for me, but it's pleasant enough, and there are periods where they run off and entertain themselves and I can relax or zone out. If your little one doesn't like picnics, just do lots of snacks and make some of them nutritious. Around 3 we'll head home, getting back by 3.30 or 4. I might set up a craft activity or get out the magnitiles or something they can do with minimal input from me - DS usually has an idea and DD goes along with it for a while. Sometimes we do some baking. And soon enough it's time for dinner, bath, bed!
It is hard, and sometimes I'm bored or frustrated about various aspects of the day, but I definitely wouldn't say I dread the weekends.
Are they in nursery/preschool during the week?