Canadian here. If you're only wanting to stay in Thailand 60 days, then just fly into Thailand as planned, you'll get 30 days visa exempt. Then extend at immigration before your 30 days are up. It's relatively easy to do on your own, so don't bother with agents. My advice is to get an online appointment (I do mine in Bangkok) and I'm in/out in 30 mins.

No you'll need the TM30 in Bangkok as well, I just extended my stay last week. Also Canadian here, it was a relatively easy experience although a long wait. The office is in IT Laksi which is an older mall accessible via SRT line. It's an air conditioned building and has lots of food options so the kids will be fine. You can get your photos taken and everything photocopied right next door on the 3rd floor. Go as early as possible though as they only give out 200 numbers to serve people.

Come to BKK and you'll be grateful for only a half day. 😅

Be smart and book an appointment online now if you're doing it in BKK, there were none available before mine expired and it literally took me all day today... maybe because yesterday was a holiday but damn it was a long day waiting. The appointment itself was less than 5 mins. 😅