I think that they are similar, but IMHO it would be easier to learn one language first, get the basics down, and then concentrate on learning others. In my experience, quite a few of the more popular languages are similar, especially the basic concepts. It's mostly just the syntax that differs.
C, C++ and C# are all very similar languages, but also very different. Most of the concepts in C were used to create C++, and likewise most of the concepts of C++ were used to create C#. I agree with Myrtle that it may be better to lean one of the two languages first before diving into the other. But each person is different and learns in different ways. If you can learn both at the same time without confusing them then more power to you.
C++, Java, C#, C all are very similar and have their own characteristic differences. It is better to get a strong hold of all the concepts first, and the learning most other languages will be just learning the points of differences between them.