I want to know that in circuits where current sources are present, KVL can be applied or not? I mean, if current source is present in a part of circuit, can we apply KVL loop including that part? Should we ignore the current source or somehow include it while applying KVL?

 

KVL effectively means that all voltage available between positive and negative is applied across the circuit. If you have 2V over part of a network between +. and -, and a 12 volt supply, you need not measure to know there is 10V across the rest. A current source is a variable voltage point in there somewhere. If you measure the voltage on any point, KVL applies.

There is a lesser known Kirchoff's current law which states that the sum of the currents in a circuit = 0. That means the current in (+) - the current out(-) =0.

 

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There is a lesser known Kirchoff's current law which states that the sum of the currents in a circuit = 0. That means the current in (+) - the current out(-) =0.

Well, not quite what you said...

The correct way of stating KCL is that the sum of all the currents into any circuit node is zero...

This, from WikiPedia:

Kirchhoff's current law (KCL)

The current entering any junction is equal to the current leaving that junction. i2 + i3 = i1 + i4
This law is also called Kirchhoff's first law, Kirchhoff's point rule, or Kirchhoff's junction rule (or nodal rule).

The principle of conservation of electric charge implies that:

At any node (junction) in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node, or:
The algebraic sum of currents in a network of conductors meeting at a point is zero.