Let us take your query in two parts -
Part I - Can Whatsapp Chat be taken as evidence?
As per Section 3 of Evidence Act,
“Evidence”.—“Evidence” means and includes—
(1) all statements which the Court permits or requires to be made before it by witnesses, in relation to matters of fact under inquiry, such statements are called oral evidence;
(2) 1[all documents including electronic records produced for the inspection of the Court], such documents are called documentary evidence.
Now as per 2(1)(t) of Information Technology Act,
Electronic Record means data, record or data generated, image or sound stored,
received or sent in an electronic form or micro film or computer generated micro fiche;
Hence in my opinion Whatsapp chat may be taken in as evidence by courts.
Part II - Will they constitute evidence for adultery
Now this is a very subjective question - It purely depends on what you have written in your whatsapp chats, in what context you have written, whether you were serious or you were in jovial mood and many many other factors.
Summary
Rather than getting into court battles, it would be in your best interests to reconcile with your wife as you have two kids.