This mention of Mephibosheth seems to be inserted here partly to show that with the death of Ish-bosheth the cause of the house of Saul became hopeless, and partly to prepare the way for the subsequent mention of him 2 Samuel 9:1-13; 2 Samuel 16:1-4; 2 Samuel 19:25.
Related Commentaries of 2 Samuel 4:4
2 Samuel 4:4
4 And Jonathan, Saul's son, had a son that was lame of his feet. He was five years old when the tidings came of Saul and Jonathan out of Jezreel, and his nurse took him up, and fled: and it came to pass, as she made haste to flee, that he fell, and became lame. And his name was Mephibosheth.b