BB is a blast. Here is what my family does at BB.
We get there early around 9 am. Pick up a Park Map as soon as you get there.
As soon as we enter the park, my DH goes to the locker area...and rents a locker. He puts his wallet and room keys in the locker. Myself and my DS (now 13) and DS friend, go to the Melt Away Bay and claim lounge chairs. We have always claimed ones near the water, but are now trying to find ones that are less crowded but close to Melt Away Bay. We find this the best location because we spend most of our time there in the little wave pool...and we can find it easliy if we decide to split up.
There is one slide we
ALWAYS go on....Team Boat Springs. It sounds perfect for your DF and their ages. It is a fun ride for the whole family!!!
When DS was younger, the age of your children, we spent lots of time at Tikes Peak and Ski Patrol. These are the kid's area. Tikes Peak is best for your 5 year old, Ski Patrol is best for your older one. There are lounge areas close to these areas...if you think you will spend most of your time here...I would head in this direction. They do have shaded areas close to Melt Away Bay if you are looking for shade.
Don't forget Cross Country Creek. We love love love this ride...it is relaxing and fun.
As far as other slides go...My DS did not warm up to the bigger slides until he was 7 or so. He did love Runoff Rapids the most...and snow stormers was a close 2nd. He loved team boat springs the best. My DH did try Slusher Gusher once.....once was enough. He loved it, but will take another few years to get his courage to do it again.
So, it really depends...where do you think you will spend the most time?
Looking for Shade: Set up by Melt Away Bay (there are spots before you reach the pool...you will see them on your way to the Bay)
Looking for Sun: Set up on Melt Away Beach
Looking for Kid fun: Set up by Kiddie Areas
And whatever you do....find the homemade mini donuts! There is a stand by the big food counter service (I forgot the name of it) Just follow the heavenly smell!
Hope this helps!!! Have fun!!
here is a map of BB:
http://www.disney.ca/vacations/disneyworld/VII/maps/pdf/bbeach.pdf