Translation:There is a little lemonade in the bottle.
When you use little or a little (pouco or um pouco) you are conveying a different attitude towards the quantity. "There is a little" has a positive meaning as in there is some. "There is little" has a negative meaning, as in not enough. http://www.edufind.com/english/grammar/few_little.php
I'm afraid my last post is causing some confusion. The two constructions ("pouco/a/os/as" e "um pouco de") has those subtle different meanings just like in English. And yes, "um pouco de" is invariable, but I believe one will only use it with a singular noum (I can't imagine right now a construction with um pouco de + plural noum. We have to check it out). However, "pouco" in this case is variable because, I think, it modifies a noum. Tem poucA água na garrafa. Tem poucAS pessoas na casa. Tem poucO vinho na garrafa. Tem poucOS pratos na mesa. But I also believe that "pouco" does not mean only "not enough". It could be only a fact concerning quantity: "Tem poucas pessoas naquela casa" doesn't imply not enough. (Could this be the difference between "little" and "few"? It's up to you, English speakers, to tell ;-)). You should notice that when "pouco" modifies a verb, then is invariable "Elas estudam pouco a língua inglesa" (I'm not sure how to translate this... sorry for my bad English :-( )
Your English is great. It's a lot better than I could ever hope to do in Portuguese! I'm guessing that your last sentence would mean "They study little of the English language" (but my translation sounds awkard to my ears, but I can't seem to come up with a better way to say it)
That's very interesting. The purists would say this sentence (tem um pouco de limonada na garrafa) is incorrect. If you want to use the verb "ter" you should say: "A garrafa tem um pouco de limonada" (the bottle has a little bit of lemonade). To be grammatically correct you should use the verb "haver" or the verb "existir" = "Há (Existe) um pouco de limonada na garrafa". But the "incorrect" form is so common that I believe is accepted as correct. In Brazil, everybody uses the verb "ter" meaning "existir".
I've noticed that when "tem" is used at the beginning of a sentence without ele, ela or você it translates as "there is." Also "You have a little of lemonade in the bottle" is not something a native English speaker would say and is grammatically incorrect. However, you could say "There is a little bit of lemonade in the bottle" or "There is a bit of lemonade in the bottle"
You can say "pouco/poucos/pouca/poucas" (must follow number and gender) or "um pouco de". The last is kind of a "fixed expression" so is invariable but is generally used before a singular noum. Note that they are not totally identical. Some posts above we discussed those subtle differences.