I try to send a box every couple of months -- or at least on the holidays. I pick up the Flat Rate boxes, which come in several sizes. No matter how much I cram into it, or how much it weighs, the cost remains the same. Shipping can be costly. I know. The Christmas box cost me a fortune. Now I try to pack it myself. Shipping stores charge 3x's the amount I pay at the Post Office. I have sent packages to my great nieces for years. Two nieces at the beginning turned into three, then into four. When my own grandchildren came along and the economy took a dive, sadly I had to cut back the number of boxes I sent to my nieces. I pick up a small box and leave it sit out for a month or so, as I collect little things to put in it. I love finding cute little things at the dollar stores and in unexpected places. Some may consider it junk, but the child in me always saw "treasure". My nieces and nephew saw it that way too. Their mom told me that once while cleaning out my nephew's room she suggested he throw out a silly pen I'd sent him. He exclaimed, "No! Aunt Laurie sent me that." It had to have been years earlier, but he remembered, and it meant something to him.
The small flat rate boxes are perfect. It doesn't take long to fill it, and the cost is minimum. The pleasure receiving it is great. Kids love getting mail. My niece told me that the kids played for weeks with the little things I sent. A little thoughtfulness goes a long way.