Child/Young Adult Book; possibly a red balloon on the cover

[Peggy]

I have been searching for a book my grandpa read to me as a child and I can't find it anywhere. Here are some details:
- At the beginning on the book a man falls in love with a girl who was a performer (dancer I believe), and her name was Mouse.
- They married and moved to a house with a brick/stone wall that separated their property from their only neighbor, which was a home for orphans or disabled people.
- Mouse was outside when a red balloon/ball went over the fence and she met some if the tenants and later befriends them
- One of the tenants was a young boy who was left there by his parents because he was too scrawny. To combat this, he would pick up things on the table to get stronger u til he eventually picked up the whole table
- Another two tenets we're self deamed couch potatoes (that resembled potatoes), and after befriending Mouse gave her a couch potato badge of some sort
- There was a protagonist, possibly a murderer, who Mouse and the tenants had to stop, but my mind is fuzzy on the details.
- "Wall" may be in the title

Please, if you have any ideas on what this could be I would greatly appreciate it. Thanks!

[Tab]

How many years ago did you read this book?
What time period/location did the story take place?
Were there illustrations in this book?

[Lobstergirl, au gratin]

Peggy, are you still looking for this or did you find it?