We use a potette like this one https://www.amazon.co.uk/Potette-Plus-Folding-Travel-Trainer/dp/B001RH2RW4 it is great and easy to carry around if there aren’t toilets nearby. We used this with our first child and currently going through with the second child. We find it is best to ask over and over again if they need to go to the toilet and reward them accordingly when they do it, but not be critical if they do have an accident.