Children don't have to be treated identically.

They're not the same and your treatment should reflect their different qualities and needs.

Give according to need
Instead of worrying about giving equal amounts, give according to the needs of each child. If one complains when you spend time on his sister's homework, explain she needs more help today and, when he needs extra help, he will get it too. Don't stop helping the one who needs it just so that you spend an equal amount of time with her brother.

Don't allow your children to pressure you into measuring and assessing everything so that it's 'fair'. If they complain about something trivial, ignore it if you can - and laugh it off if you can't. Be emphatic that if they don't stop, neither will get any.

Try putting their complaints in context: 'Some children don't have anything to eat at all. That's not fair! Complaining he's got more chips is nothing.'

Acknowledge the feeling but state your case
Sulking because he didn't get presents on his sister's birthday? Tell him you know he feels a bit left out but it's her special day. When his birthday comes he'll have lots of presents of his own.

The facts of life
Your responsibility as a parent isn't to make everything right all the time but to prepare your children for life. There will be differences in treatment and your children will be disappointed, but they can learn to deal with it. It's a valuable lesson to learn.

Note... Obviously, you sometimes treat them identically but when there's a need for different treatment, don't let them nag or make you feel guilty. Don't get trapped into justifying yourself.