Single parenting is never an easy situation. A lot of times people are put down for being a single parent. Many times folks pigeonhole single parents and they presume that their kids will not be as well off as kids in a 2 parent household. This has been demonstrated to be wrong.
Before presuming anything, people need to look into the reasons why a person might be a single parent and the challenges they confront that a 2 parent situation may not.

Divorced Single Parent

A large number of single parents are single because they have experienced a divorce. They still have the other parent, in most instances, that helps them out financially and is there for the children. Single parenting as a divorced parent can be hard, depending on the split up and the situations surrounding it.

Many times children in this situation have experienced a terrible situation when their parents split up. They may need to be assured that they are not the reason their parents broke up. Let them know that you love them every bit as much now, as you did before the divorce.

Widowed Single Parent

When the other parent passes away, the remaining parent is left in a single parenting situation. It's likely the parent never thought they would be in a situation to deal with single parenting. In addition to trying to deal with being a single parent they also are trying to deal with their grief and help their kids deal with the loss. Being a single parent due to the death of a partner can be devastating, emotionally and financially. Kids may need help dealing with the loss and adapting to having one parent. The parent may need extra help trying to deal with their own emotions and feelings about the state of affairs. They will not have the other parent around to help them in any way and they are truly on their own. Honestly, this situation is the one least likely to cause people to try and look down on you. If anything, most people will sympathize and offer to help.

Traditional Unmarried Single Parent

Broadly speaking, most people consider a person a single parent if they were never wedded to the child's other parent. This is the typical single parent situation, and it grows more common (and acceptable) every day. They usually were in a relationship with the other parent at some point, but things just didn't work out and they ended up breaking up. This situation can be similar to a divorce situation. A single parent in this situation, though, has the advantage of the fact that they knew since they were not married that they could at some point end up a single parent. However, that does not make it less challenging. This situation is the one where a person will find the most people who make judgements about the morals of the parent - and as a result that parent's fitness to raise children.

The most important thing in any of the above situations is to remember you're a parent first, single second. Don't bother trying to justify yourself or the situation you're in to people who look down on you. No amount of talk or justification is going to change the minds of people who don't approve of someone else. Content yourself with proving to yourself and your children that they were lucky they had you to push through the situation. Always insist on being the best parent you can, and you can stand straight and be proud, regardless of your circumstances.