From David Crystal, The Cambridge Encyclopedia of Language (Cambridge: Cambridge University Press, 1987), p. 289:

"For several hundred years, cases have been reported of children who have been reared in the wild by animals or kept isolated from all social contact. These cases are listed below, adapted from Lucien Malson's Wolf Children (1972). Sometimes the information is based on little more than a brief press report. At other times, the cases have been studied in detail - in particular, the stories of Victor, Kaspar Hauser, Amala and Kamala, and Genie.

"The ideas of Psamtik I [an Egyptian king who, in the 7th century B.C.E., gave two new-born infants to the care of shepherds with the instructions that they should not be taught to speak, so as to observe which language they spoke first; he concluded from this experiment that the language of Phrygia (now in central Turkey) was the oldest human language -- the story is retold by Herodotus] receive no support at all from these children. Only some of the reports say anything about the children's language abilities, and the picture is quite clear: none could speak at all, and most had no comprehension of speech.

"Most attempts to teach them to speak failed. The cases of 1694, 1731, and 1767 (Fraumark) are said to have learned some speech, and Tomko of Hungary (also 1767) is reputed to have learned both Slovak and German. The 1717 girl and the 19th-century Bankipur child are both said to have learned some sign language. But of the well-attested cases, the results are not impressive. Victor, the 'Wild Boy of Aveyron', remained unable to speak, though he could understand and read to some extent. [The only words Victor ever learned to say were "lait" (milk) and "O Dieu" (O God), though he learned to read quite a number of words. Victor died in 1828, at approximately the age of 40, ten years before Dr. Itard. -- MKJ] Kamala of Midnapore learned some speech and sign. The two most successful cases on record are Kaspar Hauser, whose speech became quite advanced, and Genie, who learned a few words immediately after discovery, and whose subsequent progress in speech was considerable."

Recorded cases of child isolation
Child known as...Date of discoveryAge at discovery
Wolf-child of Hesse 1344 7
Wolf-child of Wetteravia 1344 12
Bear-child of Lithuania 1661 12
Sheep-child of Ireland 1672 16
Calf-child of Bamberg cl680 ?
Bear-child of Lithuania 1694 10
Bear-child of Lithuania ? 12
Kidnapped Dutch girl 1717 19
Two boys of Pyrenees 1719 ?
Peter of Hanover 1724 13
Girl from Sogny 1731 10
Jean of Liège ? 21
Tomko of Hungary 1767 ?
Bear-girl of Fraumark 1767 18
Victor of Aveyron 1799 11
Kaspar Hauser of Nuremberg 1828 17
Sow-girl of Salzburg ? 22
Child of Husanpur 1843 ?
Child of Sultanpur 1843 ?
Child of Sultanpur 1848 ?
Child of Chupra ? ?
Child of Bankipur ? ?
Pig-boy of Holland ? ?
Wolf-child of Holland ? ?
Wolf-child of Sekandra 1872 6
Child of Sekandra 1874 10
Wolf-child of Kronstadt ? 23
Child of Lucknow 1876 ?
Child of Jalpaiguri 1892 8
Child of Batsipur 1893 14
Child of Sultanpur 1895 ?
Snow-hen of Justedal ? 12
Amala of Midnapore 1920 2
Kamala of Midnapore 1920 8
Leopard-child of India 1920 ?
Wolf-child of Maiwana 1927 ?
Wolf-child of Jhansi 1933 ?
Leopard-child of Dihungi ? 8
Child of Casamance 1930s 16
Assicia of Liberia 1930s ?
Confined child of Pennsylvania 1938 6
Confined child of Ohio 1940 ?
Gazelle-child of Syria 1946 ?
Child of New Delhi 1954 12
Gazelle-child of Mauritania 1960 ?
Ape-child of Teheran 1961 14
Genie, U .S .A. 1970 13 ½
If this subject interests you, there is a vast and fascinating literature on the case of Genie.

See Andrew Ward's website on feral children for additional links.