It's not a school nursery it's the sort you use while you go to work, so it's not like sending him to school on his birthday IYSWIM.
DH and I are fully capable of taking the day off and spending it with him but TBH it's in the school holidays and going anywhere like the zoo etc will be a proper ball ache as everywhere will be packed.
If he goes in to nursery they will make a fuss, I'll send in party bags and a cake and they have little parties on birthdays so he'll most likely have a great time.
I'll probably still take the day off so I can pick him up early and bring him home for presents and maybe get the grandparents over for tea too.
DH and I will probably take him somewhere a few weeks earlier as a birthday treat instead to avoid the holidays.
I feel guilty planning a day off in his birthday when he still has to go to nursery..... But he'll never know will he? 