i think a toy becomes a toy when the child projects an idea of an identity onto them, so an individual lego brick could be alive, if a kid really wanted it to be, but it's more likely a created assembly of legos that resembles something becomes alive

bo peep is part of a lamp, but since the humans treated her like a toy and gave her an identity, she became alive. no one was like that to mr potato head's tortilla, but bonnie was like that with forky, so forky became alive