Youngster is a synonym of Child. Child is related to Person. Person is related to Lap. you are likely to find Cat in/at/on Lap. 
Bit is derived from Rear. Bit is related to Mouth. Tooth is part of Mouth. Tooth is related to Inside. 
Youngster <--Synonym--> Child <--RelatedTo--> Person <--RelatedTo--> Lap <--AtLocation-- Cat 
Rear <--DerivedFrom-- Bit <--RelatedTo--> Mouth <--PartOf-- Tooth <--RelatedTo--> Inside 