For the last two years we've taken my daughter to see santa and the grinch at Pengoed Fach farms. We'll definitely be booking this year too when they sell the tickets.
There is also Santa Afternoon Tea experiences at Celtic Manor which are lovely 🎅🏼
Cefn Mably farm had a lovely meet Santa event last year too (I’m sure they’ll do something similar this year) they have a massive soft play and farm which means you can really make the day of it 😊
Bute park Christmas lights we love!
Not particularly a toddler activity but a super special Christmassy event to attend that I’m sure your toddler would love is Luminate Light Trail at Margam Park, we went last year and just loved it. A super fab sensory experience for the whole family 😊