All kids are ready at different ages, and TBH I think trying before they are ready makes things worse. My DS1 was showing all the signs of being ready by 18 months but wasn't actually ready for full time undies until just before his 3rd birthday. DS2 on the other hand trained himself just after his 2nd birthday. He pointed to a pair of DS1's undies with a picture of Lightning McQueen on the front and said "want to wear Queen". I told him to do a wee in the toilet first and he did, so I put him in the undies. He has been in undies day and night ever since! When they are ready, they are ready, and it makes life much easier if you wait until then. How do you know if they are ready - well try undies and see what happens. If it's just not clicking, wait and try again later.