Hi I'm new to this, and I have a question...my oldest (in the batman shirt) will be three March 3rd,…

Hi I'm new to this, and I have a question...my oldest (in the batman shirt) will be three March 3rd, my youngest will be one March 13th, we aren't having a bday party for my oldest but a small get together for my youngest, how do explain that he has to share his birthday with his brother without making him feel bad?? I'm tryn to explain it to him but he keeps saying it's his birthday, is he too young to understand or am I telling him wrong? Please help, thank you :/