The shift of the kids calling their dad Walter

Did you guys notice this? Drake and Megan used to call him dad season 3 and prior but since season 4, they made it a point to call him Walter for some reason. They really made Walter a goofy character. It'd be heartwarming to still see Drake and Megan embrace him as a dad and acknowledge his goofy ways but the shift felt cold and it kinda made me sad