Dallas Arboretum
The Dallas Arboretum can be a great place to take kids. Running around is allowed and there are lots of wonderful lawns with lovely grass. A highlight when the weather is warm enough are the toad fountains. They squirt water and you get to them by walking through the lovely Crape Myrtle Alley, a path covered by a natural tree arch. The arboretum also does a lot of seasonal decorations that can be fun for kids.
The Children's Garden is definitely the coolest place to take kids. There are so many interactive exhibits and lots of water features for the hot summer days. There is a small splash pad right at the Garden entrance, so get soaked first to cool off for the rest of your adventure. If you have younger kids, the First Adventure area is awesome. There is a river, a splash pad, and lots of small-kid sized play things. This was probably my favorite part of the Children's Garden and I would recommend visiting it on the way in and the way out. Other areas where you can get wet are the Pure Energy and Earth Cycles sections.
Pure Energy has lots of levers and pumps to manipulate to get water flowing in a water table. It's cool to see the different flows and the water splashes out plenty to cool you off. The Earth Cycles section has a small waterfall as well as a stalagmite and stalactite that have a drop of water dripping down to demonstrate how they are created. There is also a water table with fake sand, trees, a river button, and a rainfall button to demonstrate how water erodes land over time. The rain and river are really fun to play and you can easily splash some water on you to cool down.
There is a "treehouse" section where kids can bounce and climb on rope structures. It is fun to look down and see how high up you are!
The exhibits tend to be very STEM oriented. They are great for kids to play with at any age level. The Exploration Center is better for older kids, the labs are only available for kids 6 and up and the rest of the exhibits are also designed for older kids.
The arboretum has lots of events that you can check out via this link. My personal favorite is the Kelley Family Days. The Kelley family pays for everyone who enters the Children's Garden, which is normally an additional $3 per person.
Though on the more expensive end for admission, there are discounts to be found. City of Dallas residents can get up to 8 free tickets by asking at any Dallas Recreation Center. There are discount days available, and if you know someone with a membership they can usually get guests in for free.
If you are going to the Children's Garden, park in lot 4, the parking deck, which will be on the right as you come from the south. There is a walkway that leads you under the road on the lowest level and straight up to checkin.
The Dallas Arboretum is a lovely way to get outside in the middle of the city and kids are sure to find plenty to do. Just make sure they respect the plants!