I lived there for about 4 years, long before moving out west. August of course can be rather HOT and humid, and you can count on a vicious afternoon thunderstorm every day. Still, if you can arrange your visits to theme parks super early in the day (7AM arrival times at gates) and plan on the inevitable storm, which will likely drive your family back to your hotels' poolside.
Then post-storm you might have the rental car idling in the parking lot, and make your way toward the eastcoast of state New Smyrna maybe (about an hour/half away) and have a pre-booked Captain waiting on-standby to take you out for an evening fishing saltwater..?
As far as large mouth bass there are several nice lakes and ponds right around the parks that have some nice fish big in them. Try to do as much rekon now on where you'll stay; as its possible you might get a hotel with its' own bass-lake on the same property?
I dont think you'll find Peacock anywhere in Orlando, but I could be mistaken. Dont have advice other than that on fishing. I know theres more FL guys on here who can help better, but threw-in what I could.
Lastly a bit of common advice, buy SPF 50 and dont try to get 'a savage tan' your first day - to later impress your mates back home else; you might not be able to move on about your third. Also, no matter how tempting it seems- with offers of "Free Theme Park Tickets" under any circumstances whatsoever; accept an invitation 'to an hour tour of some bloody timeshare' while your there
DONT DO IT!!
If you fall into this trap, not only will your kids not see Mickey but you wont see any fishing either
...and might even get back to England and realize you bought a $15,000.00 timeshare while you were there, but only have two huge beachtowels to show for it?!
Good luck and have fun!
Moe Bird Hunts