How to account for parents loan for downpayment?

These are referred to as "gift funds" - but it sounds like this is actually a loan from your parents. When you meet with a loan officer they will ask what loans you have out, and the lender will take into account the loans you already have (e.g. a car loan), this will factor in to how much a lender can get you approved for. If your parents are going to gift you the money, you want to put that into your bank account 3 months prior to buying a house, or you may need a letter from your parents stating that you are not required to pay it back - so the lender can allow you to use this money.

Lenders usually require it to be documented either as a formal loan with repayment terms or as a gift with a signed gift letter. Undocumented funds can delay or deny approval.

You might want to look into the Freddie Mac Home Possible Mortgage in regards to your question. sf.freddiemac.com/homepossible

In most cases, you cannot easily get a loan for a downpayment unless you ask the lender ahead of time and the lender approves it based on the type of loan you are seeking. A loan means it needs to be paid back, your parents may need to "gift" you the funds vs "loan" you the funds. Ask your lender, they will tell you. Then its up to your parental relationship how this works.