The original reason for children not to use the finger scanner was that growth in their fingers since the last vacation resulted in different scan data.
The new scan data (one-finger scanners versus the older two-finger scanners) relies more on the fingerprint rather than the finger size and may be less affected by childrens' growth.
Also the vast majority of tickets sold nowadays do not ahve non-expiration added, so a child's growth does not come into play.
(Scan data is digested down to a single 3 or 4 digit number and it is not possible to recreate a fingerprint using it.)