Our kids will be nearly 4 and 26 month old twins -- we are bringing several bottles of bubbles -- that will entertain all 3 of them for hours should we need it. However, we're going to read Tourguide Mike to avoid the lines altogether (if it's possible)....
Please do not blow bubbles in lines! Some people (my DD included) are skin-allergic to bubble solution. If someone was blowing bubbles in a line we were in, and a bubble popped on her, we'd have to get out of line, rush to the nearest ladies room, and wash her skin off with a ton of water.
Also, stray bubbles can cause a lot of trouble with little ones - kids can dash under the queue lines after a stray bubble a lot faster than a parent can follow. Bubble solution can also stain fine clothing, and make an awful, slippery mess if they spill.

When I read posts saying how crowded a certain park was on a certain day, I turn to Mike immediately. Sure enough, it's usually a park that he advised to stay away from on that day. 