If your child isn't talking a lot it could be for a number of different reasons. The first thing to note is, what age? How old is your child? Being able to know how many words your child should be saying at each age is the first step. For example, if your child is two and only saying two to four word sentences well in fact, that's what they should be saying. So that's typically, that's totally normal and fine.
If they're older and they're not talking a lot, are they able to? Are they able to talk to you, but are they not talking to their friends? Could it be that are they shy and they don't have the skill set yet to engage with their peers? And perhaps you need to model and show them and work on those skills or do they not have language skills? Are they not able to communicate with you effectively?
If that is the case that is cause for concern and you should discuss that with your child's pediatrician. Perhaps they need a speech and language therapist to fully evaluate their language and communication abilities. This is something that can be done at any age. Sometimes children have some language but have a harder time advancing their language skills.
So just because they're able to talk maybe by the age of five, six or seven, they're not able to say increase their vocabulary and say greater sentences and as descriptive that could then mean that perhaps they're having some language barriers and that doesn't mean that they don't understand the language like English, it means that they're having communication difficulties. They could have difficulties with processing. They could have difficulties with finding the words and getting them out. And these are valid concerns that you should address with your pediatrician that perhaps would require a further speech and language evaluation.