Been down this road with both of our kids, both now in their late teens.
Honestly, just assume you need unlimited texting. If you think otherwise, well, you'll soon find out that, yeah, you need unlimited texting. Just trust me on that.
Kids don't really care much about talking on the phone anymore - texting is king, so don't waste your money on a plan with many minutes, focus on text only for the most part. My experience over many years is that both Bell and Fido offer text-only plans for around $15/month with unlimited text, and (if necessary) emergency pay-per-minute calling.
Over 4 or 5 years the text only option served us well and we NEVER needed to ever call them...honestly, texts work better anyways as if the kids are indisposed at the moment you call, a text will always be waiting there for them, but a call can be missed.
Neither had data for many years.
Last summer my son (who's now working fulltime in a trade) decided he wanted data, so he went to Wind, and my daughter followed suit just after Christmas taking advantage of their $30 promotion. Both are reasonably happy with it (it ain't perfect, but it's also half the money of the Big 3) and they retained their unlimited texting, but also got unlimited talk (which neither rarely use) as well as the data plan.
Anyone looking for a referral to Wind (Er, Freedom mobile now), send me a PM - there's $20 in it for you, and $20 for my wife's account.
If you're looking for just a "Emergency use only" phone, well...it's hard - as others have mentioned, there are options out there, but there's two problems with that approach IMHO;
1- Kids won't carry a phone that "Doesn't do anything" to them, so it'll just get left behind at home, school...and perhaps even lost.
2- They WILL give the number out and their friends WILL start texting them on it. The temptation to respond will be overwhelming, and then they're exhaust any credit on the "emergency" plans in short order. In the end, it'd likely have been less expensive to just go with a more traditional prepaid unlimited texting plan in the end, and you'll find yourself in much better communication in the end. And your kids will NEVER leave their phone behind.