To combat this, one week before you switch the clocks back or forwards, start to shift their schedule, in 10-15 minute increments. If bedtime is at 7 PM, make it 7:10 PM, then 7:20 PM, etc. every evening They'll adjust more fluidly come the day the clocks actually shift. Now this makes sense, and sounds easy enough to do on paper. But when you're actually trying to get your toddler to go to bed just at any consistent time at all, after dinner, a bath, playtime, TV time, story time, and a song before bed, it's darn near impossible.
Don't worry though – you'll get used to waking up an hour earlier after a week or so.