I had as translation "After whom is that child". I'm not sure whether this is correct english - it was not accepted at least - but I found it hard to find the official translation through the dictionary hints. How does "to take after" translate to czech? And shouldn't the dictionary hints then say "take after"?
Take after is one of those expressions that do not have any close translation. The closest Czech version by meaning is 'BÝT PO NĚKOM'. My son takes after me - Můj syn je po mně.
He is after his father. Ended up in jail. = On je po svém otci. Skončil ve vězení....
I am guessing that you are suggesting that "who" should be "whom." As it happens, "Whom does the child take after?" is also accepted. If that's not what you meant, you can let us know, as VladaFu said.