Losing a parent is a difficult thing to go through at any age or stage of life, but for obvious reasons, it can be especially upsetting for children. The sudden removal of somebody who has likely been one of the most important people they know is never easy to cope with while they are still developing emotionally, and on top of that, they have the stress of dealing with how those around them deal with the loss as well.
Unfortunately, it is not uncommon for parents to lose a partner and then react to or move on from that in ways that are traumatic for their kids. Perhaps at the top of the list in this scenario is remarrying at a time that seems inappropriate or to somebody who makes their home situation worse in some way. In these cases, sometimes the only way out of the mess seems to be the kindness of extended family.