Smart contract between mom and child to pay child when the child confirms that his tooth has fallen out. The mom can confirm the validity through the contract and the contract will pay the child.

ToothFairy.sol

pragma solidity ^0.4.18;

contract ToothFairy {
    address owner ;
    address mom = 0xd2dE66A09F48A96b8cd429951ca70F79715beBCc;
    address child = 0x80bFb3c5C9386e687936868A79f2e626F38a4AC2;
    
    bool paymentStatusToChild = false;
    
    enum ToothStatus {Mouth, WaitingForApproval, Fallen}
    ToothStatus public toothStatus;
    
    function ToothFairy() public payable {
        owner = msg.sender;
    }
    
    function () public payable {
        
    }
    
    function kill() public onlyOwner {
        selfdestruct(owner);
    }

    modifier onlyOwner {
        require(msg.sender == owner);
        _;
    }
    
    modifier onlyChild {
        require(msg.sender == child);
        _;
    }
    
    modifier onlyMom {
        require(msg.sender == mom);
        _;
    }
    
    function checkTooth() public onlyChild {
        require(toothStatus == ToothStatus.Mouth);
        toothStatus = ToothStatus.Fallen;
    }
    
    function momApproved() public onlyMom {
        require(toothStatus == ToothStatus.Fallen && paymentStatusToChild == false);
        child.transfer(this.balance);
        paymentStatusToChild = true;
    }
}