Ayrivynne Elias is a cutie! Reasons below. :>
Aipom (shiny) - Elias is lighthearted and always smiling, so that brings Aipom to mind! It has lots of energy and a good nature, so I think it would be perfect for contests. Since he's into the contest scene, no doubt that he was out shiny hunting to get himself an eye-catching 'mon. I imagine he was maybe looking for a different one, but this cutie popped up instead!
Indeedee - Indeedee shares Elias' caring nature, and female Indeedee even act as nannies to children and other Pokemon. If Elias ever has to go anywhere and can't take his team with him for whatever reason, it should put his worrying mostly at ease knowing that Indeedee is looking after everyone.
Roselia - I left his Roselia as is because I think it's a good fit for him! He seems kind and patient, and pretty handsome to boot. A beautiful, serene looking Roselia would look right at home with him. Plus it's perfect for contests and rather iconic for them if you've watched the Diamond and Pearl seasons of the anime.
Volbeat and Illumise - Speaking of the anime, know what the anime has? Doubles contests!! Volbeat and Illumise are made for each other so they'd be a hit on a doubles stage. They work wonderfully together, but also could hold their own going solo. He seems like a hard worker, so I think these busy, buzzy little guys are a good match.
Teddiursa - While not technically categorized as a baby Pokemon, just look at it! It's a li'l bear cub and it's sooo cute. It's young, adorable, and is just starting out in the world... kind've like Elias! Since Elias is already treating his own Pokemon like children, maybe when he's older he'll settle down and start a family? And by then his Teddiursa will probably be an Ursaring. A big, loving papa bear just like him. <3