Shetland sheepdogs do generally get along with other dogs, but they can be nervous around children. Early training and socialization around children can help minimize this tendency and make them more comfortable around kids.
Shelties typically get along better with older or quieter children. They have a sensitive temperament and can be frightened or overwhelmed by fast movements and loud noises, which can make them a poor fit for a home with toddlers. Sheltie puppies often naturally attempt to herd small children, and their owners must train them not to do so or it can escalate to a bite.
Shelties can also be quite loud, which can wake up napping children. A properly exercised and trained Sheltie should not bark all the time, but they tend to bark whenever they see something or someone strange in their home.
Some bloodlines within the breed are known for being particularly shy or sensitive, and dogs from these lines are less likely to get along well with small children. Families with young children may also have better luck adopting an adult Sheltie rather than a puppy, since puppies can have unpredictable personalities.
Shelties generally have a peaceful, non-aggressive temperament, which makes them calm and safe around other dogs and around new people. They have a lot of energy, so playing with other dogs can help tire them out.