Open houses are a good opportunity for you to meet personally with the seller and their listing agent so take advantage of this moment to get the details that will help you decide if you will push through with making an offer or look elsewhere. Here's 3 questions you definitely need to ask as a prospective buyer:
Buying a house is probably the biggest investment you'll ever make and it's best to be critical on where you could possibly put a big amount of your money and time on. Open houses are designed to please your senses - there are fancy lights, newly-painted walls, fragrant candles, you name it! But there might be issues on areas you can't spot right on such as issues with the roof (ask what material the roof is made of; tile and slate roofs last 50+ years, while asphalt shingles last 15-20 years), wiring, sewage, drainage, heating and air-conditioning systems etc. You can opt to do the investigation yourself while touring the house, and if you've spotted issues that the listing agent did not disclose upon your asking - low water pressure, dripping sinks, subflooring covered by a fancy carpet -- that might be a sign to step back. Also ask if the home appliances and systems are covered by a home warranty. Keep in mind that it is required by the law for sellers to disclose to buyers any code violations or structural issues. You can ask for written seller's disclosure and take photos of problem areas so you could review them when you make your offer.
You can find this information on your own but asking the listing agent can put the information in context. If it's been on the market for a long time, you could have more bargaining power. But it could be that the sellers had a previous transaction with a buyer whose financing fell through. In the case where the house has been on sale for only a short while, there might be a sling of buyers expressing interest. The information you get will be useful when you make your deal.
It's good to know information about people you will be surrounded with for a good lot of time in your family's life. Ask details that correspond to your lifestyle, like if the neighborhood is kid-friendly, or if it's congenial to retirees. Also ask about nearby schools, hospitals, police and fire stations and make your own research on their credibility and efficiency.