First, my sincere condolences.
You can claim him as a dependent for 2018 and it would be beneficial to do so as it would lower you tax bill.
You can also deduct those medical bills, if you itemize your deductions.
According to the IRS, you can claim a dependent who died during the year if you would have been entitled to claim them as a dependent if they would have survived through the end of the year.
See this explanation from IRS Publication 501:
Death or birth. A person who died during the year, but lived with you as a member of your household until death, will meet this test. The same is true for a child who was born during the year and lived with you as a member of your household for the rest of the year. The test is also met if a child lived with you as a member of your household except for any required hospital stay following birth.
If your dependent died during the year, even though he was born during the year, and you can claim his as a dependent.
