have fun wherever you go!!
there are lots of trails in arlington, irving, dallas.
https://www.sixflags.com/overtexas
since i rarely visit arlington, i dont have any recommendations for you there.
how far are you willing to drive for things?
downtown dallas has
* the Perot Science Musuem ($17 for adults, $11 for kids 2-17)
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http://www.perotmuseum.org/
* the dallas world aquarium ($21+tax Adult, $15+tax kids 2 thru 12)
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http://www.dwazoo.com/
* the Pioneer Plaza w/ larger than lifesize longhorns and three cowboys
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http://www.visitdallas.com/listings/Pioneer-Plaza/6851/
* the Reunion tower ($14 for adults, $6 for kids 4-12) - kinda pricey, imho
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http://www.reuniontower.com/
grapevine mills mall [north of DFW airport] has a Legoland place ($16-21 for everyone over 3yrs)
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http://www.legolanddiscoverycenter.com/dallasfw/
fort worth has several musuems, including a Science & Hisotry museum and a Cowgirls museum. if the weather is nice, there is also the Water Gardens downtown and Sundance square for restaurants and relaxation.