to prefer 'What'? to 'Pardon?'

[wolfhound]

although neither of them are very good. 'Pardon?' sounds a bit Hyacinth Bucket IMO, and 'What?' can sound rude.
What do you teach your DCs to say?
DS1 (3.5) seems to have adopted his own style of bellowing 'Can you say that a bit louder?' which may not be the ideal long term style.

"Ta" is dialect though.

"Ta" is definitely dialect -where I come from, all children are taught Ta before they can speak properly, thank you later, but most of us still use Ta as adults.
(mainly to friends and family - not politely!!)

I love "Ta". Though I have also taught them thank you.

I also taught DDs TTFN - Ta Ta for now (bye for now) and "See you later alligator...in a while crocodile" because I'm silly like that and it amuses me.

I love Ta ta

and I always do See you later Alligator (although I had to teach it to DH properly - he's 49 and always thought you both said "see you later alligator )

You need to play him the song by Bill Haley and the Comets!

yes, that's a fab song!