Well I had bought Wallace and Gromit DVDs and they are subtitled. Also Reader's Digest did sell a couple of "Wind in the Willows" DVDs ( the animation with Rick Mayall's voice for Mr Toad ) and they did have subtitles but they are no longer sold by RD. I once hired a Harry Potter DVD ( Goblet of Fire ) and that was subbed too.
So I conclude that the most popular ones are most likely to be subbed. I think the logic of not having subs for children's DVDs on the grounds that they can't read yet is rather dubious as there are deaf parents of hearing children who may watch them with their children and would need to know what has been said in order to reassure or reinforce lessons.
Unless the British education system is so dire that school leavers can't read at all which rather defeats subtitles!

Oh and I recently bought a Morph DVD as a 4th birthday present for a hearing child and that has NO subs but then again who can hear Morph clearly????