Seeking expert counseling is a sign of strength. A personal relationship with a caring professional is proven clinically effective.
I believe that I can help with this situation.
A four-year-old child has very little concept of such abstract thoughts such as hating his life.
You must judge him by his actions, which are that he appears to be a happy and loveable child.
You must also examine his environment: he has great parents.
He has heard this phrase somewhere else, perhaps TV or even a cartoon. The character might say it when they feel mopey or they are not getting exactly what they want.
It seems that there is no depth of meaning to this phrase. He is just saying it because of some minor disappointment. Children live so much more in the here and now, and when things are not going well they might verbalize it.
It seems as if he probably DOES love his life and that is what he demonstrates most of the time.
If he says it again, just ask him why. Don't ask him now, but only if those words come out of his mouth. Then you will convince yourself that nothing is wrong.
You are a wonderful uncle and a great blessing to him that you are alert to his possible needs and problems.
In this case, I urge you not to worry. I believe that there are no problems of any consequences, but rather the little momentary angst of a toddler overstating a situation with a catch phrase that he does not understand or feel.
I shall keep your family in my prayers.
Elliott, MAE, LPCC, NCC, CCMHC
Thank you very much for such a detailed answer you have been a great help and relief