You will only get catchlights if there is something bright for the eyes to reflect.
As Phil says, the simplest way of getting catchlights in this case would have been to use a bounce card.
Alternatively, you could have bounced your flash off a surface (maybe behind you?) which would have produced catchlights.
That said, nobody cares about catchlights except a few people on internet lighting forums (with one exception that I know of - see below).
I have sold god knows how many photos to the subjects of those photos. Some had three catchlights, some two, some one, and some had none.
The only person who has
ever mentioned catchlights to me was my sister in law, who insisted that I remove catchlights from every single photo of her daughters - because they didn't look "natural".
Have you shown the photos you took to the children's parents? If so, did any of them mention the lack of catchlights?
I thought not...
