I’ve seen this movie when I was a child so it’s probably going to be older than 2008 or so.
The only things I remember are that there was a monster that came out of the ocean but the military killed it. I believe it left a baby at the shore and the dad (together with what I believe was an older sibling) came to take the mother’s corpse back to the sea and search for the baby. If I remember correctly in the end they found the baby and returned to the sea together.
The creatures were big and lizard/dinosaur like.