Guangzhou Shenzhen to Hong Kong?

Hi all,
The wife and I are taking to little guy to Canada in December to celebrate Christmas, see the big son, and watch Star Wars and need some travel arice.
We are taking the loooong train from Harbin to Guangzhou as it's an adventure and the little loves trains.
My questions pertain to the next step in getting to Hong Kong.
We have to fly from Hong Kong due to my sons status.
What's the best way to get from luohu in Shenzhen to the airport including crossing the border.
We will have to take the train from Guangzhou east to Shenzhen but after that we aren't sure of the best ideas.
Travel options, times, and costs are what we are looking for.
The easiest idiot proof way is the best even if it's more expensive.
Thanks,in advance.

With bags?

The last time I went from Luohu to the airport, I had two bags, one on my back and one in my arms. Never again. Also, if I were going direct to the airport, I'd probably choose different transport. I walked across the border and hiked to the Luohu MTR. I say hiked because as I recall, it's a longish walk. Anyway, caught the MTR to Kowloon, stayed there overnight, then caught the Airport Express from the Kowloon station in the morning. The only advantages to this procedure are: (1) the growth and development of back, leg and arm musculature, (2) Kowloon, (3) you can do your flight check in at the Kowloon station and leave your bags there.

All in all, probably not recommended with bags and children. Probably not recommended for adults either. Isn't there a direct ferry from Luohu to the airport?

A friend has recommended taking a van which take us to and pick us up after the border and then drop us at the airport.
We will have bags and the little guy so a convenient pick up from luohu train station is worth the money.

Should add that our flight is at 4:30 pm and while not exactly pressed for time we don't want to waste it.