What times does your dh work?
Even if he needs to work as self employed, can he start a fraction later or finish earlier?
If so then he could take them out after breakfast each morning for ‘excercise’, bike, scooter, playground, walk in woods etc for 30-45mins. That way he’s used a bit of energy up if you don’t feel like going out out.
But garden play, paddling pool, would be the way to go. You can always invite a friend of yours with own similar age child over to play in garden a few times over the summer. That way you get company, child gets company, and it’s at home.
Do online food order now to stock up freezer with ice lollies for if outside.
After week or two you can probably start going out but local. Short walk to park if nearby or around on his scooter with baby in pram.
When your dh is off he can take him further afield once a week, or when he can drive you all go somewhere like national trust where you can sit with baby in shade if needed and he does the chase child part