Not all are always wonderkids in name, but they really deliver whenever I sign them.
I put my preferred players first and my second choices, should I have one, in brackets.
GK: Silviu Lung Jr. (Alphonse Areola)
DL: Joao Paulo (Joe Mattock)
DR: Diego Renan
DC: Nicolas Otamendi (Badstuber)
DC: Miles Addison (Marek Suchy)
MC: Fabian Delph (Marco Verratti)
MC: Sandro (Eduardo Salvio, Per Cilian Skjelbred)
AML: Sergio Mota (Radja Nainggolan)
AMR: Andrea Russotto (Giuliano)
ST(Target): Tomas Necid (Lacina Traore)
ST(Poacher): Andrej Kramaric (Adailton)
They might not be the very best, but they can all be realistically signed if you're not one of the top 5 teams in the world (except Delph who might be a bit tricky at first).
Off course my favorite wonderkid was Pascal, a Spanish left-back that forced Bale on the bench at the tender age of 17, but he was a regen.....
GK : Oscar Ustari
DR : Diego Renan >> never try this one, but i believe this one would be great ...
DL : Joe Mattock
DC : Nicolas Otamendi
DC : Mamadou Sakho >> never try on FM 2010, but was a great player on FM 2009
DM : Sandro
MC : Verratti
MC : Sergio Canales
AMR : Pedro Leon
AML : Juan Angel Albin
SC : Alexandre Pato >> never try this one too ...
gk - asenjo - i swear lloris is like 23 or something? not rly a wonderkid, but awesome
dl - diego renan
dc - m. sacko
dc - n. ortamendia
dr - d. santon
dmc - sandro
ml - angel di maria
mr - alexis sanchez
amc - m. verratti
amc - Pjanic
st - yannis tafer - i don't really class aguero or pato as wonderkids, as they're already huge stars...
Eden hazard, silvio lung jr, toni kroos, and axel witsel are pretty good too...
in my 3-1-2-1-3 (which, incredibly, works - well with the best team in the world anyway)
CB: Sakho CB: Otamendi CB: Zapata (would Piqué count as a wonderkid?)
DM: Moussa Sissoko
CM: Gourcuff (convert!) CM: Hamsik (Both attacking duties)
SC: Aguero SC: Balotelli SC: Pato