I think children aren't supposed to be in advertisement, because they often have no idea what they are participating in and its also usually not their own decision to be there. Being in advertisement can be sometimes hard and I think kids arent ready for it. Adverts are using your image in a very specific way, which can be damaging. There are situations where the ad gets viral or is just very controversial, and actors, whether its their fault or not, get to live with the consequences. An advert can affect your social life, your face can start getting recognised in public, and so much more, even the least predictable. So while taking part in it, you should be 100% sure and ready to do it, and kids are nor proper for all of that.