Hi Lisa and welcome to you, Rocco, your sister, and the new addition! I have a 4 month old Yorkie named Bo who I am crazy about. I ADORE maltese! My mom has one and my big burly dad is nuts about him. Anything their baby does, my dad says
"He's allowed!" 
He has a little shirt that says "I didn't do it". He weighs about 5 pounds and is 7 years old. Post pictures anytime! His name is Duster (my nephew's friend calls him Swiffer
). Maltese and Yorkies are very similar in size and tiny delicate bone structure. And both breeds love to cuddle. Make sure your sister doesn't become overwhelmed with the demands of a new puppy. And be sure and get the baby vet checked ASAP. Enjoy!!