If your child is taking high-potency antibiotics, your child likely has an infection that could be serious if it goes untreated. Don't stop or change antibiotics on your own - not every antibiotic is effective against every infection, so you may be doing more harm than good by switching.
Have you heard of the BRAT diet? It's often used to help patients with diarrhea. BRAT stands for bananas, rice, applesauce, and toast. You don't have to give your toddler all of those, but maybe try a few.
Also, make sure you keep your child hydrated with plenty of water. If the diarrhea gets worse or you're concerned about dehydration, take your child to the emergency room for evaluation. The best course of action is to get in touch with your doctor as soon as it's possible to do so.