It is suggested that toddlers need 10-11 hours sleep each night. If they take naps during the day, then those nap times can be added on top of that. It is a good idea to allow kids of up to 5-6 years old to at least rest, if not sleep, during the day.
You can often gauge if your toddler is getting enough sleep by his behavior during wake hours. If he is irritable, has emotional outbursts, rubs his eyes or yawns, then he is ready for a nap. He just may not be getting enough good quality sleep. Children who are regularly disturbed during sleep time also display signs of tired behavior.
If you are having issues getting your toddler to bed or ensuring they sleep all night, here are some suggestions:
1) Pre-bedtime routines. These give the signal to toddlers that it is time to be thinking of sleep. These routines should include passive activities such as quiet play, bath time, a story read to them and then into bed. Vigorous activities, stimulating TV, loud noise and the like wind kids up rather than put them into a sleepy frame of mind. There should also be a particular time they are in bed.
2) Constant calling out or getting out of bed should be discouraged. If you ensure they have been to the bathroom (older pre-schooler), set them up with their favorite Teddy, a drink nearby (for the older toddler) and the door ajar, there should be no reason for them to want to get out of bed constantly. This becomes a habit which some parents seem to indulge without realizing it. Also, a parent lying with a child until they go to sleep can also become an unnecessary habit which can go on for years!
3) Night time fears, night terrors etc. Fear of the dark can be a real issue with children. In fact, I would suggest that we have all been afraid of the dark, especially imagining things like monsters under the bed! So, no spooky night time stories. Be aware of older siblings scaring younger ones just to tease them. Watch the TV content. We soon forget the TV show's very graphic and scary scenes, even on the news. Having a night light just bright enough to show you where the child is is an excellent idea. Night terrors sometimes occur, but are often more alarming to the on-looker than the child. Do not wake the child, but just hold him close to you with the light off. Soothe them until they settle.
Some source material: Dr. Alex Bartle, Founder of Sleep Well Clinics