We also have a child with special needs and we always go to Icmeler it is about 1and half hours from Dalaman.She really enjoys herself and all the staff make her feel really special she just loves everything about Icmeler

Olu Deniz is another good option. The beach is not completely sandy, it is pebbly near the sea, but there is also the lagoon, which is very safe for children to swim in.
Lots of things to do, and trips from here. A very family friendly resort which is not too in your face. My fav holiday destination = my children love it
45 min transfer from Dalaman. IMO the most scenic resort ive been to.

susien
is that 45mins transfer by taxi or coach???
i was looking at bitez it sounds nice but the beach seem very small.

Have been both. It can be done in a taxi using the Gocek tunnel in 35 mins.
We went in a coach last year with Thomsons with no stop offs until we reached Olu Deniz and did it in just under 1 hour.
We also went on a minibus using the tunnel with no stop offs from Ovacik (3 miles inland_ and this took 45 minutes.

If you prefer a private transfer, which is obviously quicker there is someone on here who does them I think, have read it before. Will try and search the link for you.

http://www.holidaytruths.co.uk/viewtopic.php?t=3797&highlight=private+transfer+olu+deniz

Here you go read this!!

Be aware that if there are lots of drops this journey can take 2 hours. I would book a taxi transfer.
The main beach is not sandy so you would need to go to the lagoon for this.