Can there be such a thing as 'professionalism' in childhood?

It's common among coaches I interact with to refer to an absence of professionalism among their child participants. I understand what they're getting at but is it reasonable to expect adult-like behaviour in children? 
Immature behaviour in adult sports people is common place and that says two things for me: 1) stress and pressure destabilises, and 2) maturity is complex and can take decades to grasp.
The expectation of responsible, mindful behaviour in children is appropriate but it needs to be reasonable for each child. It also needs to be seen for what it is: akin to asking them to brush teeth or clean bedrooms. As adults, we need to be patient and endlessly supportive if that's what it takes.