Depending on the age of the kids, you may be better off going someplace like the Colleyville Nature Center. edit - I missed the age in the original post
I personally haven't had much luck bank fishing at Grapevine with the kiddos.
Honestly, Grapevine Lake isn't the best bank fishing lake. If you're looking to bank fish, you might try going to Parr Park or Bear Creek Park and fishing in the creek. Always a ton of sunfish, blue gill and the occasional small bass or catfish. I've found it's a lot more productive there then at the lake. Parr Park especially.
Growing up we always had luch with crappie around the matina next to oak grove fields. Other than that over by the dam was good. But it has been years since i fished Grapevine