When one child requires more attention, it can throw the family dynamic off or cause other children to adopt the negative behaviors to get increased attention. As a parent, it can be hard to navigate how to deal with all the family's needs in a way that works for everyone. When things aren't balanced, often parents feel a lot of guilt and stress, and in trying to make things fair or right with their other children, they may actually be inadvertently adding to the imbalance. 
Our children have different personalities and different needs. As a parent, we want things to be equal for our children. We think we are equal by spending equal amounts of time, giving equal attention, or dealing with them in the same way. Fair doesn't mean equal. In fact, for some children, too much time actually could make them feel anxious or nervous. What is important is that how we interact with them fulfills their needs.
Convey this idea to our children that fair doesn't mean equal is essential. Once children understand this, often attention-seeking behaviors will decrease. 
When a child requires a lot of attention, it's helpful for parents to reframe that negative behavior. Finding the positive from that behavior allows you to help them turn that into strengths instead of using it negatively. For example, suppose a child is upset. In that case, you can reframe that as they can advocate for themselves, which allows you to find opportunities where they can positively advocate for themselves.

These two things will go a long way in changing the dynamic in your family for the better.

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