@summer63 A lot of malls have indoor play spaces for little kids, and those are usually free. Can be a good option especially on rainy days and such.
Parks, playgrounds, nature centers. We live near a park so go there a lot...but I also really like driving around to check out different playgrounds- I've found some of them have more interesting equipment than others, or some are more toddler-friendly than others. Some of my local parks also have free nature centers with some toys, activities, books, and even animals inside. Sometimes these parks organize free programs for adults, families, or even like toddler and preschooler-specific events. I follow my favorite parks on FB so I can see when they post info about upcoming events.
Similarly, you can look for local events like fairs that will be happening throughout the summer. My city has a lot of different fairs and festivals, and some of them are even specifically for families and kids. I see a lot of touch-a-truck type events happening, too. Last year, we went to a local Honey Festival and I actually really liked that lol! And again, I kinda just follow local FB pages and try to keep an eye out for any events that I see being advertised.
And then I agree with the other comment about getting a membership to something like the Zoo. My MIL gets us a membership for Christmas every year, and it's great. You could also look for things like science/kid museums, indoor playgrounds, botanical gardens, aquariums, trampoline parks, etc. Just check out the prices and see if any memberships are affordable for you, or if perhaps you could request a membership (or even gift cards) in place of other holiday gifts.