I believe that LE knows (or reasonably infers) that little Kyron is deceased. That's why the case switched to a 'criminal investigation' on day 10 and why they continue to search bodies of water, rather than treating this as if he walked away. LE knows he's not coming home for 'Father's Day.' So does the family.
There's the golden rule of 48 hrs in child cases, where something like 90%+ of kids are killed within those hours, which is why it's so crucial to know ASAP when a child is missing. Valuable hours were unfortunately lost in this case. That doesn't mean Kyron could have been saved, btw, but every minute counts.
However, if a child comes to harm at the hands of a family member or caretaker, then all bets are off and no amount of time is going to matter since these things are usually premeditated in such cases.