All good advice from above but also when taking out the child to a store make sure you know where every bathroom is!! Even if they went BEFORE you left they will have to go in a store.

Don't be afraid to ask in the stores to use theirs. Remember all GAP's have bathrooms and let you use them! You can walk into the movies and use theirs(usually not very clean!). Fastfood places you can do the same. I like Nordstroms bathrooms. You have 3 children you get to know where to pee!