How about saying, that you want them to come and celebrate your birthday, then go on to say that as you have all the things you could possibly ever need, so instead bringing you a birthday gift, you would love it if they wanted to, bring along a nice toy which will be donated to the local hospice. That way you could enjoy the gift of their company on your special day and the residents of the hospice could also celebrate your birthday with a nice treat too. I must say that this is a great idea I may "pinch" it at some later date! Have a lovely birthday when it comes.