If you have access to Microsoft Office 365, Teams is certainly excellent. WebEx is OK as is Zoom.
When thinking about children as users though, you may find it easier to use Microsoft Skype (the consumer version) which many will already use when talking to relatives remotely. I wouldn't normally recommend it as a pro tool as it can be a little heavy on the network but in your case, it may be easier for everyone.
I've been working remotely on and off for many years so I've used and implemented pretty much all of the conferencing tools over that time. We've just about finished a deployment of Teams to 10,000 users. Not that this applies here but we are also integrating our room-based video and audio conferencing facilities and replacing all our desk phones with Teams.
I've been working pretty much exclusively from home since Oct. last year and often spend 4-6 hours a day on Teams and Skype for Business calls (sometimes WebEx and Zoom if a supplier organised the meeting). It isn't unusual to have remote conferences lasting 3 or 4 hours.
BTW, for anyone now facing hours on conference calls, do yourself and everyone else a big favour and get a decent USB headset. Plantronics or Jabra for example. Expect to pay about £70 or maybe more if you need the bells and whistles. These are comfortable, have noise cancelling microphones and protect your hearing as they are designed for all-day use. If you really can't stand or use headsets for some reason, get one of the conferencing speakers. Again these use noise cancelling field effect microphone arrays. It is much less tiring for you and easier for everyone else.
Agree with Nick that WebEx is a very poor user experience. Our Teams deployment has met with massive and rapid acceptance even before this crisis. Generally much easier to use than WebEx. Rather more enterprise focused though so maybe not so good for this use-case.
If you do have access to Office 365 though, Microsoft have just extended free Teams use until 2021 to allow you to have other people join your Teams for free.
Somewhat off-topic (what's new!) but we had a really successful test of Teams Live Events (supports up to 10k attendees) today for all of the Directors of Nursing (up to a thousand people). Despite being hastily put together and the fact that we were only just beginning to test it, it worked really well.
I suspect this is where you see the real difference between a global cloud service run by a global monster with money to burn and a smaller, hungry specialist.
We are currently struggling getting 120 Architects into Home Office. As we have complex CAD software handling 3D-BIM models it's not an easy task.
I'm not involved in IT in my office any more (lucky me) but the original idea was using the users privat computers as remote clients. For the first 20 Architects it worked but (as everybody who can do the math expect) getting worth with very colleague working from home. 100 VPN tunnels handling files of around 1-2GB will be difficult too and moving everything into the cloud is (very) expensive. Autodesk don`t offer there cloud sevices for free in the crisis as Mircosoft or Google does (and see a marketing possibility: once the staff is used to a good service they likely demand it in the future).
Brief update... I've tried a few packages and the one I like so far is Zoom.
It is cross-platform and very easy to set-up (see *** below). It has quite a few features like creating channels or rooms, which in my case will be very useful. I haven't tried the "schedule a meeting" feature yet, but looking at the demo videos it looks very easy to perform.
My requirement is quite modest compared with some of the things people are trying to do (as listed above).
e.g. Helping my grandchildren with their school-work (as their school closes this Friday) and keeping in touch with the students who attend my IoT Club.
(***) My grandchildren, a student from the IoT Club and a couple of personal friends managed to install Zoom and join me in a "chat" in a matter of minutes. I managed to easily share images and PDF documents (held on my PC) to the chat group. The video conferencing feature is also very impressive.
Today I'm going to try "sharing my screen" and using it as a whiteboard - just as if I was in a classroom with an LCD projector running a PowerPoint presentation.
Quick update as I've been collating video conferencing tools for others as well.
Though Google announced last year that they were closing Google Hangouts, it is still available for consumer use and supports up to 25 people any 10 of which can be on-screen at the same time. Requires a google account. Google now refer to this as "Google Hangouts Classic" to differentiate it from "Google Hangouts Chat" which, despite the name is an entirely different product.
Another one popular with teenagers is called HouseParty. This supports up to 8 people at a time. However, I don't recommend the use of this as the security and privacy policies are pretty dire.
I believe that Discord also does video chat with up to 10 people.
Snapchat supports up to 16 people I think. WhatsApp up to 4. Facebook Messenger up to 50 (only 6 on-screen at once). Instagram up to 4.
I think that Teamviewer also has video chat though I've not had a chance to look at it as yet.
Please do remember though, if you aren't paying directly, you are probably paying indirectly. Lots of these services may use adverts but also gather far more information about you than is comfortable. That information is sold on to 3rd-parties. It is particularly important to let people know this, especially parents.
At least Zoom is trying to sell you a service and is a little more enterprise focused. Google Hangouts is also a known entity and we already know how they reuse data so most of us are a little more comfortable about that.
My 2 cents as well, if I may
After having used webex for years (and a lot of pain !), we have move to bluejeans 18 months ago. Seems to be similar to zoom in term of features. With the recent WFH policy (coming from France we are all staying home at the moment), we have been hosting large meetings (more than 100 participants) nicely and efficiently. It seems to be a tad cheaper than zoom.