When babies reach 12 months old, they are ready to use a regular chair. It is when they can sit up and support their weight. At this point, they are also willing to start crawling. Some parents keep their babies in a playpen until they are 2 years old. In general, this is a good idea for babies who are not yet strong enough to sit up or crawl. A playpen allows your baby to sleep safely in a confined space and protects them from accidents. It also allows you to keep an eye on them while you are busy with other things. If your baby can sit up and crawl, removing them from the playpen is okay. However, if your baby is still too young or weak to do these things, keeping them in the playpen until they are older is best.