Depending on how much they weigh, you probably can. The recommended dose of children's liquid ibuprofen (for ages 6-8 years) is 2 tsp, and each tsp has 100mg in it. So you should be able to give them one pill. The best thing to do is talk to your local pharmacist (or your doctor), but it should be ok.
I know when my son had the flu last month (he's 10), our pharmacist told me it was ok to give him 1/2 a dose of theraflu, instead of making me buy children's tylenol and children's cold/flu meds (since they don't sell it combined anymore in a children's formula) which would have been almost 3 times as expensive as the one bottle of theraflu.
As advised verify with the pharmacy the concentration of the formula/pill. Your child is at the age when concentrates of meds change dosages change depending on weight, it just isn't something you want to make a mistake with.