I suggest that you get some guidebooks on Dubai for a better idea of things to do and see there first THEN come back here for more detailed questions to the Fodors gang.
I say this as I have noticed that any posting you have ever posted is always wanting Fodorites to plan your trip without really looking into specifics first. Just saying...
Everyone is very helpful on here but you have to have an idea what your family wants to do and see first.
The Weather Channel and guidebooks are your best source for what would be the best weather month for you.Dubai is NOT where I would go for a beach vacation but you have to realize that January in Dubai is not cold like January in a Western European country.

January overall weather would be better.
But as above, you've got to do your own research to determine whether DXB is even the place for you.

hi guys ,

i think i am being understood on this forum. i do have below the list of activities i want to do with my 4 yr old .

Dubai aqurarium
Ski dubai
Swim with Dolphin @ palm jumeira
Observation deck @ burj khalifa.....
Dubai fountains below burj khalifa
Dubai aquarium and underwater zoo @ dubai mall
The water park @ Atlantis
The big bus tour
The dhow cruise with dinner

So yes i have done my research , i am not excepting anyone on this forum to do my search . i just need to know if can i swim with my little in water parks in end of september or , would the water be too hot.

"would the water be too hot?"

Reminds me when in Cambodia with unbearable heat/humidity thinking a dip in the pool is just what we needed. Surprise, surprise, instead of being cold water... it was just like a bathtub, yet still refreshing.

So only a guess, if DXB in Sept is anything like Southeast Asia, the water maybe warmer than expected*, but not hot. Besides, I've yet tipped a toe in a kiddie pool to find it other than warm... wonder why?

*unless the Emirates have figured out how to keep it cold... ice maybe?

I fly to Dubai for work with the airlines and for me I would rather be there in January.When you get off the plane at 9pm at night and you can still see the heat searing off the pavement as you get into your limo...I don't know if the water will be too hot in September but the outside temps will still be high.
I would do the on/off bus and start it after 12 noon so you could use the tickets for two days then. There are two routes and with your little one you could do the red route one day and the blue route the second day. This ticket includes a ride on a dhow and various stopovers to see things like the Dubai museum and the souks,etc. It gives you a great way of seeing everything to know where you want to go.
Where are you coming from?

The weather in September will still be close to 100F, at the coolest upper 90s. January is the "rainy" season, at least that is what they say. It doesn't rain very often. The weather will be pleasant around 80s. I see you want to go to the Atlantis, the rates will be higher in January than September, most hotels in the UAE run specails until September 30th. Almost every hotel will also have a heated pool in January (not sure if the water park will be though). If wanting to swim in the gulf it will be cold. At least for me it is now after living here. Get your Burj Khalifa tickets ahead of time, as it is a very popular place.

thanks dutyfree and peg . i am coming frm malaysia . we have decided now to go in septemeber 26. thks for the info on the hop and hop off bus. would 5 days be suffiecient or 6 days ? i have listed above the things i want to do . thks

You can do the Burj Khalifa, Dubai Fountains and the Aquarium in one day as they are all right at the Dubai Mall. You can do the dolphins, and waterpark at the Atlantis in one day. Like dutyfree said, you can do the bus in two days. Ski Dubai is in the Mall of the Emirates, if that is the only place you want to go then that would be a half day, and do the dinner cruise at night. So in theory you can see Dubai in five days, but if you want some relaxing time then you could do six. The other thing to consider is a half day desert safari. I believe they have them for families.