As parents, you often hear about life's great injustices:

"While I was drawing, his elbow moved my hand so now my princess has a moustache!"

"She moved eight spaces instead of seven! I saw it with my own eyes."

"He ate the last lolly even though I had written on the box, 'Do not eat the last lolly!'"

You're expected to mediate, to help find a solution -- for the 17th time this morning. No more, you say. It's time call in an unbiased third party.

Hearing your kids fight is a practice in restraint. You want to jump in, bust out Mum or Dad Voice, and remind them that you didn't give them the gift of a sibling so they could spend their days screaming about whose cheese cracker is cheesier. However, as we know, there are good reasons to let kids engage in some healthy conflict.

Every parent with more than one child probably knows this secret: Kids will do a chore faster if you turn it into a competition. "Let's see who can fold the most T-shirts. Ready, go!" "I wonder who's going to brush their teeth and get into their pyjamas first. Hmmm. Go!" "You know, Mummy could use a massage. Who can give me the most amazing one? GO!"

With child siblings, there will always be fights over who gets to name the new puppy, who gets to pick out the film for Movie Night, who gets to be the green gingerbread man in Candy Land, and other matters that change as swiftly as one can cry out, "It's so not fair!" Instead of getting upset, parents can help them solve the argument peacefully by holding a chore auction.

Sometimes, a decision that's even tougher to make than "Should we have a child?" is "Should we have another child?" -- and if the answer is yes, then the question becomes "When?" Sibling age gaps, AKA birth spacing, is a massive topic of analysis -- for economists, sociologists, the World Health Organisation, and most of all, parents, who must strategically weigh factors from finances, to their careers, to the annoying "clock", to the type of relationship they envision for the kids themselves. And then of course, the decision may not be in their hands at all, as it isn't like you can simply pick a date on the calendar and type in "new baby". It's very complex and very personal.

While the subject remains taboo, most parents have a favourite child. The Wall Street Journal points to research that supports this -- in one recent study, 75 per cent of mothers confessed they felt closer to one of their adult children, while another report found that 70 per cent of fathers and 74 per cent of mothers acted on those feelings and demonstrated preferential treatment.

Where there are siblings, there is sibling rivalry, and it's usually the challenge of the parent or babysitter to keep things as harmonious as possible. To keep her sons from competing and fighting, Joanna Godard of Cup of Jo avoids assigning "roles".