I'm sure it's been asked before, but would BA permit an inflatable Travel foot rest for kids in Y?

Friends are flying to SIN, and with two little ones they obviously want to make it as comfortable for the kids to sleep as possible.

The kids would sleep in the normal seated position, so a seat belt would be attached round their waists, but I'm sure I'd read previously that things like the Jetbox were not permitted.

Any help would be much appreciated.

M