Hello and thanks you for using Just Answer. To qualify as head of household you must meet all of these tests:
1 You cannot be married at the end of the year.
2 You paid more than half the cost of keeping up your home
3 The home was the principal residence for more than half the year of either:
Your qualifying child (son, daughter, brother, sister, stepchild, eligible foster child or a descendant of any of them.
If your boyfriend's children lived with you for the entire year you can claim them as dependents but you cannot claim the head of household status unless you meet all the tests.