The Son had two different natures.
He was fully God and fully man. These two natures are "connected" via the hypostatic union.
As God, the Son was omniscient, but as man, he was not.
He was completely dependent upon the Father.
This is a rough analogy, but suppose I moved to another country and wanted to learn what it is like to be a person from this country. Suppose I could turn off my ability to understand my native language, and totally used the language of this country.
This would be a similar concept. I am not saying that Jesus never accessed his divine nature, but in essence, the idea is that he did not access the divine nature. The Father worked through Him, and he relied on the Father.
Jesus did not know the day of his return, although the Father did. This is because Jesus voluntarily limited himself during the Incarnation.
There are individuals who believe that he totally emptied himself of the divine nature, and was only a man during the Incarnation. This view is called the "kenotic Jesus". I do not hold this view. I don't believe that he totally emptied himself, but that he voluntarily limited himself with regards to his divine power.
Here's a verse the kenotic Jesus people would use:
Philippians 2:5-8 5 Have this mind among yourselves, which is yours in Christ Jesus, 6 who, though he was in the form of God, did not count equality with God a thing to be grasped, 7 but emptied himself, by taking the form of a servant, being born in the likeness of men. 8 And being found in human form, he humbled himself by becoming obedient to the point of death, even death on a cross.
(ESV Strong's)
I do not think that they are correct on this, though. I believe he limited himself in terms of his divine nature. And this is the more orthodox view within evangelical Christianity.
Regarding my position, I would point to this verse:
John 5:17-18 17 But Jesus answered them, “My Father is working until now, and I am working.” 18 This was why the Jews were seeking all the more to kill him, because not only was he breaking the Sabbath, but he was even calling God his own Father, making himself equal with God. (ESV Strong's)
Jesus was claiming that he and the Father work continually on the Sabbath. What was he talking about? The Jews knew that God did not rest on the Sabbath, because they attributed the maintenance of the creation to God, including births and deaths. Embedded within Jesus' remark was that both he and the Father are continually working, and have always been working, all the time. This points to Jesus' identity as YHVH, the Triune God.
The Jews knew what he was saying. In essence, he was claiming to be the Triune God. That is why they were enraged.
I see other hints that Jesus did not become "only a man" as the kenotic Jesus claim indicates, but that he retained a dual nature from the Incarnation up to now. He is the unique God-man.