Grammar check for a 6-year-old: 'The tip of your tongue often tastes sweetness first' — corrected and explained

Correct and simple: The tip of your tongue often tastes sweet first.

Another good way to say it: The tip of your tongue often tastes sweet things first.

Why this is better (in kid words):

1. The subject is The tip of your tongue — that's who is doing the tasting.
2. The verb is tastes — that tells what it does.
3. We say sweet (an adjective) to describe the taste. Saying "tastes sweet" is more natural than "tastes sweetness." You can also say "tastes sweet things" if you mean sweet foods.

Example: When you lick a lollipop, the tip of your tongue notices the sweet taste first.