If your baby or toddler is sleeping reasonably well and following a 7-7 routine (generally going to bed somewhere around 7PM and waking somewhere between 6.30 and 7.00AM), follow this:
Saturday do nothing differently
Sunday when the clocks have moved forwards, wake them at 6.30/7.00AM, summer time. This is an hour earlier than they would usually wake.
Put them down for their naps when they seem tired, which is likely to be half an hour to an hour later than their usual time. The last nap of the day may need to be cut short to ensure they are awake for long enough before bedtime.
Put them to bed at around 8.00PM so that they are tired enough to go to sleep, unless they are tired a little earlier.
Monday morning wake them up at 7.00AM new time and follow their normal routine on the new time, ensuring that they are awake from their final nap by the right time.
They should then fall into the new summer time within a few days.
Alternatively, you can cut back their naps on the Saturday and Sunday that the clocks go back so they are a bit more knackered than usual and wake them at 7.00AM summer time on Sunday and that will do it too.
For example:
Saturday cut naps by 50% and do normal bedtime.
Sunday wake at 7.00AM summer time and cut naps by 50%.
Child should then be tired by 7/7.30 summer time
See! Easy!