A broken bone in a small child is not in itself a sign of abuse, but I’d call it a soft marker. Along with other markers, like black eyes and UTIs, it might add up to something concerning. One of my kids fractured her leg when she was 2 - a “toddler fracture”, caused by landing in a twist after falling off the bed - and I was fully prepared to be checked out by hospital services (I wasn’t, but I would have understood if someone had talked to me)
It's largely dependent on the age of the child, too. A 2 or 3 year old is very mobile and accident prone. A 15-month-old child like Evelyn won't have been very mobile for the majority of her life, which makes it more concerning, IMO.