Samuel brought home a Mudcrab. The Mudcrab is one of many pets your kid can find and bring home in Skyrim Hearthfire.
A Mudcrab is an animal in Skyrim
 Hearthfire DLC
A Mudcrab is one of the possible pets your child can adopt in Skyrim: Hearthfire
There is a random chance your children will bring the Mud Crab home and ask you if he or she are allowed to keep it as a pet.