You set a time for him e.g. after breakfast 15-30min, and ask him to sit here few minute for defaceation. If he can sit proper, you put a sticker in the toilet.Need to train slowly & be patient.
I gave my son a book to read when he was sitting on the toilet since one year old.
Now, he is 1.5 years old la. He is willing to sit on the toilet. But surely, still sometimes poo-poo in the diapers.
I bought a potty and then we sit together in the toilet, let them know they will also do the same when the grow up, I think it's better not to use the diaper in day time,and bring them to toilet regular,e.g every 2 hours, just depends on how many fluid they drink, when they pass on the floor again & again, they will know is not good & then will run to toilet when feel urge. Don't angry if they are not willing to sit because they feel boring when they are sitting in the toilew bowl.