No, you can't. The exemption is for equipment designed solely for use by a disabled person. If the manufacturer produced an IPad which had preloaded SN software and could only have SN suitable apps loaded onto it, then it would be eligible.
An IPad bought from an apple store is for general use, even if you then use it exclusively for a child with SN:
HMRC site
"4.5.6 Computer software and hardware
Computer systems are increasingly being used as aids to disability. The systems are made up of a number of separate pieces of software and hardware. Some are general use items taxable at the standard rate of VAT, whilst others have been designed solely for use by a disabled person and are therefore eligible to be supplied at the zero rate.
....
9.2 Concession 1 - zero-rating of central processor
A central processor may be zero-rated if:
it is sold as part of a computer system; and
it has software installed, which enables a disabled person to use the computer system or other software effectively, or to carry out tasks effectively when otherwise they could not.
No other general purpose hardware may be zero-rated under this or any other concession.
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9.3 Concession 2 - Composite rate of VAT for computer systems
Traders supplying disabled people with complete computer systems that contain significant specialist items for use by disabled customers may use a composite VAT rate for such supplies. This rate will be based on supplies of such packages made by that supplier over a recent representative period.
In addition to the items of equipment designed solely for the use of a disabled person, the suppliers may include the values of the following elements of the package in the zero-rated portion:
the central processor described at paragraph 9.2; and
costs charged to the customer for the installation of the equipment and for the training in its use.
9.5 Restrictions on both concessions
The arrangements apply only to complete packages. Replacement units or upgrading items will be liable to tax at the standard rate unless they are ?designed solely? for use by disabled people when, of course, they will be zero-rated. Thus, if a customer changes the central processor, the standard rate will apply."