During a recent playdate, one of my son's white four-year-old friends looked up from Thomas the Tank Engine and pointed out the obvious. "You're black," he told my son. As a parent, these have never felt like particularly teachable moments. Toddlers have plenty of time ahead of them to acquire anxieties, affiliations and attitudes about race. But what they see primarily at their age is not race but difference – a fact that need prompt neither denial nor panic, rebuke nor rectification, unless some derogatory meaning is attached to that difference.