Dont lie to them in the first place

You explain to him that one day he too will become Santa and fill his own children’s heart with joy and anticipation. That Santa will live on through him until he passes that privilege down to his own children. Let him know that without magic in the world children would be very sad. Its hard with siblings as they always want to spoil what they no longer have. Keep your fingers crossed that this may just work.

I don’t think children should be told any lies about Santa. Go ahead and let them enjoy presents etc. and don’t worry if someone (ie older sibling) reveals what is going on. Chances are the child really wont care anyway. It will be more you that is upset thinking that some imagined fantasy has been spoilt. The kids will have fun with the presents regardless of the origin, so go ahead and have a happy christmas without stressing about the lies you think you have to tell.

I would talk to the child, tell him that he’s a big child now. And that he will have to help you keeping the magic of Christmas like you did with him. I’d ask him to help me with the preparations, maybe the choice of gifts for the smaller child, so he feels older and more in charge.