At that age they are probably happy to just spend time outdoors playing on the beach, parks or the pool.
Little Explorers in Mirdif is good and splash play in JBR.
Lost Chambers in Atlantis and even Aquaventure.
My children of that age love The Journey at Kite Beach. It's a gorgeous outdoor playground with water features they can play in. It;s 30 dirhams entry per person for 2 hours.
http://www.thejourneydubai.com/
We are also spending a lot of time at Kite Beach with the weather being so gorgeous. There are a lot of food options and a grassy area for a picnic. You can hire double kayaks for 60 dirhams an hour and they have child life jackets.
Little explorers Mirdif city Centre suitable for both & there are vouchers in the entertainer , 2 adults go in for free with 2 children. It is nice & different than other play areas.
If Sharjah is an option Al Qasba has loads of attractions like boat riding, Emirates Eye , 9 D cinema, outdoor play area, and bikes renting. They are also running a light show in the evening and there is a Turkish products bazaar those days. If you have the family entertainer there are vouchers for the emirate eye & the play areas (outdoor & the indoor one) at Qasba,
Mini golf - there is outdoor mini golf at Al majaz water front in Sharjah & there is an indoor one at wafi city
There is a dancing fountain show in Majaz waterfront, a nice outdoor play area, a track for bikes & scooters & light shows
Excellent weather to visit a feeding/petting zoo. Highly recommend emirates park zoo in al shahama. .. it's a compact zoo and kids get to feed a variety of animals quite fascinating for under 5 yrs Olds.
Maybe the Beach with buckets and spades - that works for hours! Kite beach has a new path to bring a buggy right down near the sea!
The beach at JBR is also very easy to get onto.
Al Qudra Lakes to play on the sand dunes and fly kites.
Lots of parks like Mushrif, Al Quoz Pond park, Barsha park and park at JLT for example.
Hope that helps!
Any suggestions of where to take the grandchildren when they visit next week? We are going to Dubai Aquarium and combining that trip with the fountains. Ski Dubai to see the penguin( not sure what else they can do there?)
Is it too cold for the water parks (they are from the UK so quite hardy!!)
Everything else I have found on line appears to be too old for them to do.
Help!!!