If you're not chronically disabled and incontinent, you are not eligible for VAT exemption... However sales of 200 or fewer disposable diapers/pads for personal use should be zero-rated for VAT on the shelf. The zero-rating does not apply to clothes (onesies, etc.) or accessories (wipes, lotions, etc.) -- any order containing such items will render all items chargeable for VAT, unless you are VAT exempt.
Advice and information about VAT exemption and eligibility on purchases of incontinence products.
www.allaboutincontinence.co.uk
There's a lot of confusion due to the ambiguity and vaguely contradictory nature of official HMRC advice on the issue. Clearly no one considered ABDLs! However, I think you can legitimately zero-rate diapers so long as you are honest in any declaration you make.