I would get a basket that's deep enough so the babies don't fall out, and wire it to a branch that you can reach without getting hurt. Be sure it's sturdy and won't tip over. A margarine container would work also, punch holes in the bottom (for drainage in case of rain), and the sides near the top. Run a wire though the side holes, and fasten firmly in the tree they fell from. Against the trunk will work too so long as it's secure. Watch to be sure the adults return to care for the babies, which they should. Raising baby birds is very hard to do when you don't know the species, and diet needed to keep them healthy without killing them. Better that the parents continue to raise them before it's too late. If it's impossible to fasten a makeshift nest in the tree, use a tree that's close enough that the parents hear the babies. If all else fails, call a wildlife rehabilitator to take on the remaining babies. Good luck, and hope that they make it.