A: The guy wearing a giant mouse head that severely limits his hearing and vision can't see the kid. It looks like he should be able to see her through the mouth, but if he can also see through the eyes (and his interactions with the kids on stage suggest he can) he was likely not paying attention to the view through the mouth, which was the only way he would have been able to see her.
B: Call me cynical but I wouldn't be surprised if his boss has literally trained him to avoid black kids when possible because they're more likely to damage the expensive costume.
Two most likely scenarios:
A: The guy wearing a giant mouse head that severely limits his hearing and vision can't see the kid. It looks like he should be able to see her through the mouth, but if he can also see through the eyes (and his interactions with the kids on stage suggest he can) he was likely not paying attention to the view through the mouth, which was the only way he would have been able to see her.
B: Call me cynical but I wouldn't be surprised if his boss has literally trained him to avoid black kids when possible because they're more likely to damage the expensive costume.