Dear Uncle Steve,

Sorry for not writing for so long. I just want to tell you about my birthday party and thank you for your birthday presents and money. It was very generous of you to send me £50. I want to buy a new bicycle, because my old bike is too small for me.
My birthday party was fantastic. I invited a lot of friends. We danced and ate many sweets. My mum made a delicious strawberry cake. We had a very good time.
Thanks again for the presents. Hope to see you soon.

Yours,
XYZ