You are going to find many tours offered to do this activity. My advice is to save your money and use your rental car. Most tours cost around 50-70 per person and in reality you are going to see the same thing if you drive. The reason you might want to have the tour is to do the tour that offers to bike down, but since my son it is only 7 that was not an option for us.
You will need to leave your hotel really early for this. If you are in the tour, you probably have to leave earlier, just because they stop to pick up other people on the way to the crater. If you are driving, make sure you have enough gas in your car.
You will need to leave your hotel around 3:30 am to make sure you get to the top before sunrise. Check the sunrise time because it varies depending on the season. We left at 3:30 am it is was enough time.
The road is narrow so be careful. You will need to pay $10.00 per car to enter the National Park. Keep your receipt because it is valid for 3 days and you can use it to get into the other entrance if you drive to Hana
Once you get the top, it is going to be really cold. Take jackets, blankets, pillows and even hot chocolate or coffee. There are no restaurants or shops, so take snacks and water as well.
Be prepared to wait. Little ones might want to stay in the car until it is the actual time to watch the sunrise. Make sure you know the settings on your camera to take good pictures while dark and then when the sun is coming out.
Take lots of pictures and enjoy your once in a life experience. Even you do this again, each day the sunrise is different.
On the way down, drive slow, use the low gears on the car because some cars breaks fail. My son got sick on the way down, so take some bags just in case. It is difficult to stop the car.
This is a must experience and I recommend to do this early on your trip.