It's a milestone, after all - it's the age of "chinuch", where it's possible to start actually educating a child, to introduce them to the sweetness of Torah and mitzvot. But this was different for Ezri and for his parents and all the many friends and loving relatives celebrating this day.
He was a little overwhelmed, or maybe a lot overwhelmed. He was used to a house filled with people - his parents, his sisters, nannies and therapists, his grandparents and aunt and uncles and all of his parents' many, many friends and their kids, because his parents are generous and hospitable and their family is very close. But this was more than usual - the house overflowing with people, many of whom he'd never met, and filled with noise and shouting. But there were familiar people and there were people singing to him, and Ezri loves music. Ezri was named for a psalm his parents loved to sing, and parents do have the spirit of prophecy when they name their children.
But there was something else filling that house. Normally, a upshersin is a happy event, with a cute child getting his hair snipped so long as he has patience for it (one little cousin of mine actually snipped his own, with his father's help) and with the promise of a future of torah, chuppah and massim tovim (learning, marriage and good deeds) ahead of him. But mostly, it's just an oversized birthday party with a hair cut involved, and possibly a bit of a ceremony, as he's given an aleph-beis, a beginning Hebrew alphabet book, with honey smeared on the letters so he should know learning is sweet. (Usually, that happens after the little boy is carried to his school while wrapped in his father's tallis (prayer shawl).)
Of course, Ezri didn't know that. He probably sensed the feeling through the house - not just celebration, but a fierce joy. Because, you see, two weeks after he was born, he became extremely ill. In fact, it was a miracle he survived at all. And he did not survive unscathed - he is developementally delayed. He doesn't speak, his vision is very impaired and his motor skills are poor. Even his head is out of proportion small, although that's not visible under his golden curls.
All Ezri knows is that his father spoke for a long time while holding him in his arms, and then his mother spoke and cried a little, and then there was singing and dancing - and all those strange people sang his favorite song (Ring a round a rosy) and then they sang the song with his name in it. He didn't know that all the children came in to sing a song about the aleph beis, or that the book he was given with the honey, the book with large print and braille, was the aleph beis (but he wasn't all *that* fond of the honey), but he knew that he was dancing in Daddy's arms and then when people snipped at his hair (not too short at his mother's request), he was being held by a grandpa.
But this little boy who could have died at two weeks was here with us. And so everything he does, every milestone he hits, is a blessing and a miracle and that's how his parents see it. They love him for who he is, and rejoice at whatever progress he makes - and that he is already doing good deeds just by existing. And so they were celebrating him - as he is.