Once a few years ago, late on a frozen Maine winter night, my daughter came into my study, crying, and opened the shoe box she was carrying, and inside was her pet rat, stone dead. She loved that little thing.
I commiserated and said how sorry I was. I said put her somewhere safe and I will bury her tomorrow. She just said "I can't do that..." and right away I knew--I was burying it that night.
The ground was frozen. Rock frozen. I picked a good spot, one I knew was very sandy, and got to work, with my daughter holding a flashlight so I could see. It was about 20 degrees and the ground was so hard I couldn't actually shovel it. I had to use a garden trowel instead. I would stab at the ground a few times with the trowel then scoop away what I had dislodged. Then repeat. I wanted it done right so the hole had to be deep enough. That was about 2 and a half feet. I don't know how long it took but it was more than an hour. After we had buried it I took her to my big garden which is bordered with rocks that are about half the size of a basketball. I said, pick your favorite, and she picked a nice beautifully smoothed round bright white one. That was put on top of the grave to mark it.
I just remember the feeling when I realized--I wasn't going to be waiting till the next day to do that task. She was so visibly sad that it automatically flipped a switch and I just said "okay tonight it is then! get a flashlight so you can help."