Learn Dutch: Zelfs de kinderen begrijpen het. - Even the children understand it.

Zelfs means "even" (as in "even the children"). Zelf without the -s means "self" or "myself/yourself" (as in ik doe het zelf - "I do it myself"). Adding that one letter completely changes the meaning!

Why isn't the word order inverted? Shouldn't starting with the adverb Zelfs push the verb in front of the subject?

Usually, starting a sentence with an extra word or adverb triggers inversion, swapping the subject and the verb. However, here Zelfs is attached directly to de kinderen to form a single, grouped subject: Zelfs de kinderen ("Even the children"). Because this entire subject takes up the first position, the verb begrijpen stays in its normal second position.

Why is the plural of kind written as kinderen?

The word kind (child) is a very common irregular noun. Instead of just adding -en or -s to make it plural, it takes the special ending -eren. Another common example of this is ei (egg) becoming eieren.

Could I use dat instead of het at the end of this sentence?

Yes, but it changes the focus slightly. Het simply means "it", referring to a general fact or situation in a neutral way. If you use dat, it means "that" (Zelfs de kinderen begrijpen dat), which places a much stronger emphasis on the specific thing being understood.