Getting a child a chemistry set is an excellent way to introduce principles of chemistry. However, not all chemistry sets are created equal. Keep in mind the child's age and emotional maturity/responsibility, the amount of supervision that will be available when the kit is being used, and the availability of kit contents for replacement. Chemistry sets also vary widely in price.
Chemistry Set Pricing
Cost of the set is not necessarily an indication of its quality. There are some excellent chemistry sets with low price tags because the materials are not included in the kits. Of course, there are different prices for the same item depending on the seller, so comparison shop!
Recommended Age of a Chemistry Set
All sets are designed with specific age groups in mind. Today's chemistry sets are designed by educators and scientists as much as by toy manufacturers, so the lower age limits are pretty accurate. Keep in mind that an older or independent child may prefer the option to explore chemistry rather than follow instructions for results. Kits are available in both forms.
For some chemistry sets adult supervision is recommended; for other kits adult supervision is required for safe operation. Supervision recommendations are based on toxicity of chemicals and fumes, fire or burn hazard, use of breakable items, etc. Basically, adult supervision is a matter of safety rather than of explaining instructions.
Chemistry Set Refills
Most chemistry sets are one-shot investments. Once the chemicals are gone they may be difficult to replace. Some kits are designed for use with common household substances. These kits have staying power, but may not offer some of the 'cool' effects that require specialized chemicals.