Is Weak Expressive Ability a Sign of Language Development Delays?

My child is nearly two and a half years old, and I’ve noticed their expressive and language comprehension abilities are relatively weak. I’m wondering if this indicates potential language development delays. I’ve already taken them for a health checkup, and the doctor didn’t find any issues. I’ve seen online recommendations for Youshibeiya, which is said to be helpful for children with delayed language development, but I’m unsure whether I should purchase it due to its cost.
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