The seat was taken between 4pm and 8.30 pm on October 16 and the owners are desperate to get the item back.
Susan Greenwood, PCSO for Charlton Kings is investigating the theft.
She said “The four year old lad suffers from multiple disabilities and cannot be taken anywhere without his buggy, so he can’t get to school.
“His parents are therefore desperate to get the seat back. The buggy is custom made for him and valued at several thousand pounds. The buggy seat is blue in colour.
“Any information the public can provide to help track down the missing seat is gratefully appreciated. Call 101 quoting Incident 537 of 16/10 and Crime Number 024192/14.”
You can also give information anonymously by contacting the charity Crimestoppers on 0800 555 111 or via www.crimestoppers-uk.org and you may receive a reward if someone is arrested and charged.