Required to File Gift Tax Form when Purchasing a Home with our Child?

My husband and I purchased a home with our daughter last year.  All 3 of our names are on the deed and on the mortgage.  My daughter lives in the home.  My husband and I paid the down payment at time of purchase and we pay the mortgage.   Are we required to file a gift tax form since we paid the full amount of the down payment, and if so, how much is the "gift"?  Is it 1/3 of the down payment since there are 3 owners?  Is it 1/3 of the purchase price of the home?  And if we pay the home off early in a few years, would we then be required to file a gift tax form for 1/3 the pay-off amount (assuming my husband and I pay off the mortgage and my daughter does not contribute)?