The box jellyfish found in in-shore waters around northern Australia during the summer months is potentially fatal, but stings from most jellyfish are simply rather painful. Calamine lotion, antihistamines and analgesics may reduce the reaction and relieve the pain. Spots of blood on bedclothes or on the wall around the bed can be read as a suggestion to find another hotel. Bedbugs leave itchy bites in neat rows. Calamine lotion may help.
All lice cause itching and discomfort.
They are caught through direct contact with infected people or by sharing combs, clothing and the like. Your children's contact with local children may well be closer than your own contact with the locals so be prepared. You may think it's a good idea to carry an appropriate treatment shampoo with you. Infected clothing should be washed in very hot water. Salt or a lighted cigarette end will make them fall off.