Sharing vs Taking Turns in Early Childhood Education

Depending on the age, whether the child has siblings, and situation in the home, a toddler or a preschooler may have a period adjustment in a social situation such as a home daycare or preschool. Montessori calls it a period of "normalizing", or getting used to the social environment.
this requires positive adult guidance and interaction.
Some preschool teacher's believe sharing is a natural occurrence in toddler's and preschoolers and a loving act. It is actually more so developmental and learned-more likely to occur when a child's basic needs are met.
Basic needs of a child:
Well fed/and hydrated 
Diaper changed/body feels comfortable 
Child feels safe and loved

Sharing is considered a to be more a milestone in development than manners for little ones in early childhood programs like mine. When children have positive feelings about sharing it is usually because of a positive environment as well as hitting a milestone in their development.
Supervising and being observant of preschoolers and toddlers is very important. I am often there to narrate their actions for them because so often I see them misinterpreting a loving hug as an assault or vise versa. I encourage taking turns, letting them work out the reasonable amount of time they wish to take a turn-then commending them for sharing when they follow through with the turn taking. Yes.....it takes time. The reward comes when after a while the scenario plays out like this...

"I want to ride bike, Jada." Taylor says.

"Um..5 more minutes, okay?" Says Jada.

"No, 3 more minutes." Says Taylor.

"Okay..." Says Jada. "Come get me." (Taylor runs off to play in the sand).

Jada rides the bike for five more minutes then goes to get Taylor in the sand box.

"Taylor, I done, get your bike!"

"Thanks, Jada!" They high-five each other and switch places.