Buy a pretty bucket (or paint and decorate one that you have) Then cut out some love hearts and flowers on cards. When your child "fills a bucket" give them a card to drop in their bucket. You can write on the card if you want to remember it, (particularly if it was something sweet that they said) You can put these cards in their keepsake boxes at a later date.
But don't forget if your child is unkind they must remove a card from their bucket.
You can give them incentives a treat for filling the bucket, money or some time with mummy doing what they want!
You explain to your child that everybody has a kindness bucket, and when it is full, that person is happy, they are fun to be with and everybody wants to be their friend.
The bucket is very easy to fill up, for example if you smile at some one and say "good morning" your bucket is filled a little and so is the bucket of the person you smiled at. If you do a good deed and pick up something off the floor, clear the plates, get a drink or share your sweets the bucket fills up some more.
The downside is that the bucket will also empty. If you are rude, your bucket will empty. If you push past some one, don't stop to say good morning, don't do what you are asked your bucket will also empty.
The problem is that people with empty "kindness buckets" are often sad and angry, they become even more sad because no one wants to be their friend.
This is why it is so important to have a full kindness bucket and to help others fill theirs.
I have three children living at home and while I mostly rejoice at their unique and individual characters, there are days when I simply despair at the fact they hurt each other. (Mostly unintentionally).
The two youngest siblings are very close in age and really get on well, with the exception that their characters and way of handling situations are very different.
Michael who is 14 months older than Kitty is very loving and will always put everyone first before himself, my daughter doesn't think about anyone but herself. When Michael says "kitty I love you" she will always reply with "well I don't love you". I have tried everything to make her see how much these few words hurt her brother, but in vain.
Finally I came across a book called "the kindness bucket" and used this concept to explain. The visualization seems to work and we saw a marked improvement in her actions and words immediately. It is certainly a "no solve all" but it has helped.