L.C.
Hi, M.,
I looked at your profile to see the ages of your boys and it says 4 and 2. I am assuming they haven't grown too much since you made made your profile description. They are still close enough in age and your 4 year old is still young enough that some of those toys (which I am assuming it's mostly toys) your younger son has still look pretty fun and engaging. I would start by saying, "If you would like to play with them, I am sure your brother can share. Would you like to look at them?" If they aren't witheld from him (not that I am assuming they are) then there isn't all that much to envy.
Another thing is, when he starts to make his statements, redirect the conversation to what toys of his own he particularly likes. Ask him what his favorite things are from possessions to games, shows, ways to spend his time. When he answers tell him, "Wow! What a blessed boy you are! You have all those things to like!" When he starts to speak with envy, redirect his thoughts and words to gratitude and it will become habit.
Hope this helps,
L.