Arnica is great for bruises, and so is St. John's Wort (Hypericum). I keep them both on hand all the time, and they're great for a range of small injuries (avoid broken skin). Some cosmetic surgeons even recommend it. The sooner they are applied after injury, the better, but they will even help older bruises resolve faster.
I got slammed in the face by a young goat a few years ago, and by the time I got to my bathroom my eye had swollen almost closed, with huge bruises spreading up my forehead. It was bad. I started applying arnica and hypericum, alternating between the two every 20 minutes. Four hours later, there was no sign of a black eye, no bruising, no swelling, and very little tenderness. There was only a small tear in the skin under my eyebrow.
You can buy these ingredients separately or combined, suspended in oil or various creams and salves. You can also get tiny homeopathic pellets to melt under the tongue, which can be pleasantly distracting to a child crying from pain. I think they all work well, but my favorite has always been the suspension in olive oil. I've found this at several different health food stores.