When it comes to parenting, I think there are some general principles that we can draw from the way God the Father treats his children. That is why I am not, in principle, opposed to various types of punishments for our children when they are disobedient. A spanking may be the best, most appropriate way to deal with sin in our young children (Prov. 23:13), but withholding privileges, for example, may also be a suitable punishment.
What about promising our children rewards for obedience, with the intention of motivating them to do what we ask?
Here I believe we may look at the way in which God rewards his children and appropriately, with great care and wisdom, apply this principle to the way we raise our children.
Given the plethora of teaching in the Scripture on rewards for good works (Rev. 22:12; Matt. 16:27; 25:14-30; Lk. 19:11-27; 2 Cor. 5:10; Heb. 11:26), I'm surprised the topic does not surface more than it does. God rewards our good works (WCF 16.6). Of course, we cannot merit rewards from good works because these good works are graciously given to us to do from eternity (Eph. 2:9-10). And the issue is not whether God rewards our good works, but can rewards for good works motivate us in any way?
It may be that some think that promising rewards for obedience leads to a slavish spirit. Anticipating this objection, John Owen acknowledges that some think "to yield holy obedience unto God with respect unto rewards and punishments is servile, and becomes not the free spirit of the children of God."
In response to this objection, Owen asserts that such a reaction is a "vain" imagination. Only the bondage of our spirits can make what we do servile. "But," says Owen, "a due respect unto God's promises and threatenings is a principal part of our liberty." He argues that in the new covenant the hope of rewards, for example, is actually a liberating motive for holiness.
Those who are made partakers of the covenant of grace, and make use of the means of grace that God has appointed for believers, may find comfort in the fact that they will not fail to perform the obedience required by God "merely for want of power and spiritual strength" (2 Pet. 1:3; Matt. 11:30; 1 John 5:3).
The very fact that God promises rewards to his children will necessarily motivate his children to seek these rewards. How could we be indifferent to such promises? We would be disobedient children if we did not, in some measure, seek that which is so clearly promised in God's word.
How, then, does this relate to parenting?
Parents, if they are able, naturally want to bless and reward their children. There is always a fine line between good theology and bad theology, and that line is perhaps a lot finer than we'd like to imagine. Some parents may seem to only be able to get their children to obey by either promising the child something if he/she does what is requested or by issuing a harsh threat (e.g., raising their voice even louder). Sometimes the parenting style is nothing more than a perpetual form of bribery, which ends up enslaving not only the parents, but also the children.
Our children need to know that they need to obey simply because this pleases the Lord (Col. 3:20). Even here, there is the motivation to please the Lord. Nonetheless, arriving at the place where they are only prepared to do something if they are promised this or that is a dangerous place to be.
Yet, that doesn't necessarily mean we cannot motivate our children by sometimes promising them a reward for their obedience. Godly wisdom from the parents will, of course, dictate how often and the nature of the reward; but the principle itself is a way - not the way - to help our children obey.
Returning to my original point, our Father in heaven has promised to reward us for things done in the body during this life (assuming they meet the requirements for what constitutes a good work). While we need to be careful in this matter, I think parents should, as they are able, learn to reward their children in appropriate ways so that they can teach their children, tangibly, what our Father in heaven is like towards his children. While there are many unconditional promises, there are plenty of conditional ("if you do this then ....") promises (and warnings) made to God's people.
To expect our children always to obey without ever promising a reward may be a case of provoking them to wrath. And here, as earthly parents, we may end up very much unlike our heavenly Father.
God loves his children and delights to reward them for their imperfect obedience. Should we be any different with our own children?