Complex sentence: A child who is sensitive may be distracted by a door slamming and will not be able to maintain focus, whereas a child who tends to not be sensitive to external noises will be able to maintain their focus.
Split into simpler sentences: A child who is sensitive may be distracted by a door slamming and will not be able to maintain focus. Whereas a child who tends to not be sensitive to external noises; they are able to maintain their focus.