Can small children have kidney problems?

Very much so. Children can be born with congenital kidney problems of various dgerees of severity & can develop kiney problems as small children. Children can have polycystic, multicystic or dysplastic kidneys. Horseshoe or ectopic kidneys. Hydronephrotic obstructed kidneys either in single or one segment or both segments of a duplex kidney. Pyelonephritis, glomerulonephtitis, hemolytic- uremic syndrome, etc.