The clock is like a car going around a round about. It can only go one way, there's a car (big hand) and a Lorry, little hand. Because the lorry's bigger, it goes slowly. The car goes all the way round and back to the top in 60 minutes, the lorry takes 12 hours. This teaches them the difference between the minute and hour hands, and the direction.
The imagine the round about is a cake. The cake gets chopped in half, to get from the top to the bottom is half the cake, so this is half an hour. If the cake is chopped into quarters, this is quarter of an hour.
The minute hands are more complicated. There are 60 minutes in an hour, pretend these are miles around the round about. When the car starts at the top (12), it takes it 5 minutes to get to the next number, which is why it is five past whatever number the hour hand (lorry) is at. There are 5 minute differences between all of the numbers, which is why people say 25 past, 10 past etc. It means that the big hand (car) has gone thin number of minutes past the number 12 (top of the round about). When the car (big hand) has got half way around the round about we stop saying past and start saying to because it's going towards the next hour.
I have probably missed things off so you may have to carry this on. Hope it helps (sorry if it confuses you). It worked with my ds. Best to take it in stages, learn the way the cars move first, then the half past and hour, then quarter past, then the rest. Good luck.