I notoriously have no child characters but I can offer Ben Crouch, Flight Instructor for the fall and J. Alfred Darrow, Sailing Instructor for the summer, if he's inclined to hang around the Sanditon.

Also he's not played rn but Thom Pettigrew has gone through phases of giving all the Black kids gifts like he's a more present version of their dad and he has two kids who are somewhere vaguely in this age range.