"dotykać" in its literal, physical sense takes Genitive. For most neuter nouns, Nominative plural and Genitive singular is identical. So yes, "cookies" = "ciasteczka", but in Nominative. And as you need Genitive here, "ciasteczka" has to be Genitive singular. One cookie only.
The Nominative plural is "ciasteczka", and if you wanted to use "my cookies" in this sentence, that would be "Ty dotykasz moich ciasteczek".