Watters Creek in Allen has a Lucky Duck club for kids usually on the 2nd Sat of the month and there are fun activities. Last week they had hayrides, pony rides, petting zoo. Sometimes they have balloon artists and face painting. Our group of cheerleaders volunteered last year for the events to help children with arts and crafts and loved it.
We loved going to the Dallas Arboretum. Beautiful flowers, a kid play area, ,you can picnic if you want.
Heard Museum in McKinney has nature trails and some exhibits.
Squiggley's Playhouse in Garland (Beltline/Plano Rd), is a fun place. My daughter is 16 and happened to meet the owners at hobby lobby while she was buying supplies for an upcoming project. She and her friend ended up going to the playhouse to work on their project. They have art classes, pottery wheels, mosiacs and lots of things that are fun!
I've never been here but I've heard there is a place in McKinney called Storybook Farm whith hayrides, gunfights, etc
Celebration Park in Allen has some water sprayers that are fun.
Dallas World Aquarium, Science Place at Fair Park
Wildflower Festival in May (Richardson) is a lot of fun
Balloon Festival in Plano (Sept) is also very good.
Check out the free magazines Dallas Child, etc... they have lots of good ideas.