Thank you for the reply. Do you know how long after you make the online application you are asked to go and pay? And is the interview something detailed and serious? No worries if you don't know. I appreciate the effort.
It's very relaxed here in regards to bringing your kids places. Maybe there's a place to learn Thai that also has a space for your kid to be when you're in lessons.
The list of potential problems and dangers of traveling by bus from Bangkok to Phnom Penh are endless. I'd highly suggest to fly and save yourself trouble.