With 9 year olds I wouldn't spend too much time on rebounding drills, but a few here and there are certainly a good idea.

Here are a few rebounding links with drills and tips:
http://www.breakthroughbasketball.com/fundamentals/rebounding.html
http://www.breakthroughbasketball.com/drills/basketballdrills.html#reboundingdrills

Personally, I would keep doing the fundamental stuff in practice and then just start tracking Defensive Rebounding Percentage. Share that with the team. Set a few goals. That will get them thinking about it and simply sharing it will improve your teams rebounding (even if you don't do any drills).

Here's an excerpt from our rebounding ebook (http://www.breakthroughbasketball.com/pr/rebounding.html)

"Just as importantly, you need to review and emphasize the RIGHT statistics. Most coaches, players, and fans look at Number of Rebounds and Rebounding Margin.

However, those two statistics are very misleading.

As an example, let’s say your team shoots 30% from the field and your opponent shoots 60% from the field. Your team had 20 offensive rebounds and your opponent only had 14 offensive rebounds.

Based on those statistics it seems that you out rebounded your opponent and your team did a good job on the offensive glass. But that’s NOT the case!

The other team actually did a better job of offensive rebounding. Your opponent didn’t have very many opportunities because they shot such a high percentage. But your team had twice as many offensive rebounding opportunities because you shot such a low percentage.

So in reality, the Rebounding Margin statistic has very little value. That’s why we prefer rebounding statistics that are based on the percentage of opportunities.

The TEAM Rebounding Statistics You Should Be Using

Here are the rebounding statistics that you should use and emphasize:

• Defensive Rebounding Percentage (DRB%)
• Offensive Rebounding Percentage (ORB%)

These stats are based on opportunities and they give you a true indication of your rebounding performance.

To figure your Defensive Rebounding Percentage, just divide your team’s defensive rebounds by the sum of your defensive rebounds, plus your opponent's offensive rebounds:

DRB% = DefReb / (DefReb + OppOffReb)

Now, to see which team did a better job defensive rebounding, you just compare your team’s defensive rebounding percentage to your opponents. If your team has a higher percentage, you did a better job on the defensive boards.

To figure your Offensive Rebounding Percentage, just divide your team’s offensive rebounds by the sum of your offensive rebounds, plus your opponent's defensive rebounds:

ORB% = OffReb / (OffReb + OppDefReb)

Your Team Goals and How to Use these Stats

DRB% and ORB% are the two most important rebounding stats for you to emphasize and watch.

For every game you play, your goal should be to have a higher offensive and defensive rebounding percentage than your opponent. Those goals should drive your entire plan to develop a great rebounding team.

The purpose of your practice plans and all your rebounding drills should be to improve those two percentages.

We suggest that you set some specific team goals. Your exact goal depends on your situations and has to be realistic for your team and their abilities. But as an example, your goals could be to have a 5% higher offensive and defensive rebounding percentage than every team you play.

If you accomplish that, you know that you have a good rebounding team and you’re winning the war on the boards.

Another goal could be to simply improve your rebounding percentage. To do that, you’ll need a “baseline”. So, if you’ve been at 68% defensive rebounding percentage on average, then your goal could be to move up to 72% in the next three weeks.

Don’t be afraid to set goals. They will help you get better."