Good With Dogs:⬛⬛⬛⬛⬜⬜⬜
The Morkie or Maltese/Yorkshire Terrier cross is a very human dependent breed of dog. They do not like being alone and can become destructive, depressed, bark and get anxiety if left alone for too long. Puppies should never be left alone in a crate longer then 2 - 3 hours at a time. If you plan on getting a puppy, make sure there is someone such as a friend or family member that can come and let the puppy out every couple of hours. You may want to look into a Dog Walker to come to your home if you can not find a schedule that works for everyone, including the puppy.
I had a Morkie up until recently due to a freak accident. We are both military and gone 12 hours a day. All of our children are in school and the pup was always home with just my 11 year old cat. I never had any anxiety issues with him. He was probably the best dog (breed) you could ever want. He was great with kids (6-16), the cat...not so much the chickens, but they held their own since they were bigger lol! I would recommend a Morkie to anyone!
The Maltese/Yorkshire Terrier cross should do just fine around your grandchildren as long as the puppy is not played with too roughly and ends up not liking children. All interactions between children and a puppy/dog should be supervised at all times. Allow the puppy to have a safe place, such as a bed or crate in which it means that the puppy/dog is off limits to children so the puppy/dog knows that it can go there if the children get too much for it.
As long as neither parties are aggressive they should play well together. Senior Morkies may need more space than puppies.
The Maltese averages in at 6 1/2 - 9 pounds, while the Yorkshire Terrier averages in at 4 - 6 pounds. So it all depends on if the puppy takes after the Maltese or the Yorkshire Terrier for weight. But it could be anywhere from 4 - 9 lbs obviously. As for fur, that again will also depend on if the dog takes after the Maltese or the Yorkie. If you are dead set on the long silky fur, then I wouldn't count on the cross, as most have the shorter/curly fur. I would get a purebred Yorkshire Terrier if I were you.
If the dog was socialized with children, then the dog should be fine around the four year old. But all interactions between the child and dog should be supervised at all times. The Morkie / Yorktese is a delicate dog and can easily be injured by a rough child or rough play.