Translation:I have a few clothes for your child.
Because a couple implies two and the plural noun "clothes" is not countable in English. It is incorrect to say three clothes or five clothes and clothes does not even exist in the singular.
Things become a little more complicated because you can say many clothes, which is normally not possible for uncountable nouns, leading to much debate on forums as to whether clothes is countable.
You would also use a couple as following, if it were correct... "I have a couple of books for you", "I have a couple of hours to spare"
On a final note, the given translation "I have a few clothes for your child" does not sound as good as "I have some clothes for your child" to my native ear.
Hope this helps.