It's important to recognize the hard work of your children and what could be better than an interesting fun filled reward of their choice. When they make you proud it's your turn to make them happy as this is a powerful motivator.
However before assigning them any work you should rate personally whether it's realistic and achievable? The expectations you set should be reasonable and reachable. Ultimately, your approach is to set your kids for success without making things too easy or too difficult, to give them a sense of achievement.
While choosing a reward option you should be very careful as you're setting an example and expectation for your child. Let's check out what all could be the fruitful reward option.
An extensive reward for a small task can set a wrong example in front of your child and might lead to more trouble than benefit in future. Promise a valuable reward on daily basis, for example, offer an extra bedtime story or even delayed bedtime as possible rewards, your child's favorite dish could be an interesting option. This will not only set their expectation correct but will also help your kids learn to appreciate the little things in life.
For some greater achievements of your child like good grades in final exam or if they have won some inter school competition, acknowledge their success with some interesting and big reward. Kids love celebrating with their friends. Reward your child with a surprise party with their close friends. Your child will love you for this and will always feel motivated in future assignments.
In case both of you're working and hardly get quality time to spend with your kids, "your time" is the best reward for your child. Take a day off or plan a vacation and spend a fun time with your child. Play their favorite sports and cook their favorite dinner. Even you'll have the inner satisfaction and this will undoubtedly create a strong bond between you and your child.
The most important thing, make sure it's done in a timely manner as you're idol for your children. If you'll not follow rules they'll also take you seriously in future. On the other hand, if your child does not deliver on his end of the deal, it's important you be little strict and don't reward them as promised. Remember, you're teaching the importance of follow-through and the meaning of commitment.