At 3 and a half, I think that he will very quickly be able to tell when he's wet or dirty if he only wore jocks. Let him have the responsibility of telling you himself when he has or when he needs to go.

I think pull ups are over hyped personally, although I did like the pull up swimmers.

Never ask him if he needs to go. Instead, tell him to let you know when he needs to go to the toilet - again giving him the responsibility. I know it might seem harsh to some, but they really do enjoy having some form of control over themselves at this age

With DS, we went cold turkey. Got rid of nappies all together. He had a couple of wee accidents in the first 4 hours, and then not again. He certainly worked out very quickly what the full bladder feeling meant. As for #2's - that took 2 weeks total but he had bowel issues beforehand that didn't help.

A sticker chart in the toilet room itself was a huge help (especially with #2's) and it helped to keep the reward associated with the act of going to the toilet. My son gets distracted so easily and I figured if we left the reward until 10-15 mins later, he may not associate it with the correct behavior I was trying to reward

My number 1 tip? Don't stress If he sees how trouble free you are about it, he's likely not to stress out and catch on very quickly.

I hope that helps and good luck!!