Three of my children will have their birthdays this coming month. My oldest will be 11 on the 24th, my son 6 on the 25th, & my youngest 4 on the 27th.
A couple of years ago I did an afterschool party on Friday for my oldest daughter & her friends. We made tie dye shirts & had pizza in the backyard - it was lot of fun! Then at about 5:30 I had our family over after work to celebrate all three birthdays. It worked out great for everyone.
To give everyone something special I made each one their own cake & decorated it the way each one wanted. Also my youngest picked out a pinata and my son picked out the candy bags. My daughter who's birthday is in May went shopping, only her & me, for the birthday gifts.
This year we are doing a family party with a friend or two. Not sure the details yet, but will always try to make them their own cake. I feel like this means a lot to them. And of course sending the cupcakes to school & celebrating each birthday on the exact day; by singing to them first thing in the morning & at dinner time. They all think they get two birthdays!
Hope this helps, I love to plan parties! Let me know if you need ideas.