1) Anesthesia has more risk in children compared to adults. There are many reasons for this including simple concepts such as the small size of the windpipe in the very young child. Cardiac events and even death are risks in any anesthesia and these are higher in young children- however, remember that anesthesia is very, very safe but the risks are somewhat higher in young children compared to adults.
2) One of the concerns is the risk of learning delays or 'cognitive' difficulties for children that have surgery at a young age. This is very difficult to study for some obvious reasons including only young children with serious issues have major or repeated surgeries at a young age. There really is very limited know risk to simple, short surgeries such as ear tubes or short orthopedic surgeries. A very good study was published from Sweden on this topic.