2 small kidneys. Transplantation of very small kidneys is challenging because of the small blood vessels in which the blood flow may become blocked (from blood clots) and because they may not have enough function to support a large adult. If the recipient is carefully selected and understands these risks, it may be highly appropriate to use both kidneys together (en bloc), which optimizes both of these factors.
No. I'm sure a transplant surgeon would go on about how it may fulfill some of the needs, but the truth is it's just too small to take on the full load of an adult. Plus there are simply way too many children needing a renal transplant who need an infant sized kidney. Unos would likely not allow a non-directed donation, and I don't know any transplant surgeons who would allow a directed one.
Yes. Many transplant surgeons transplant both kidneys from small children under age 4 into an adult (called en bloc). The youngest donors are most often over 9 months of age, but a few have been done using younger infants. They can work quite well and will grow larger in the adult recipient. They are placed in the same position in the lower abdomen near the bladder as are full adult kidneys.