UK is the only country in Europe where kids cannot ride e-bikes legally although those are allowed to be sold in UK. 24" wheels bikes are suitable for children below 14 years old, however only 14 years old or older are allowed to ride an e-bike in UK legally at the moment.
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I ride an e-bike myself and everytime I go out with my son (who is 11 years old) he wishes he had one as well, so I looked into it. Unfortunately, I cannot get him one even though they are for sale in UK. He is very disappointed. I also found that the e-bike weighs exactly same as his non-ebike which is 18kg so that would not affect him anyway but would help him to keep up with me and my partner and enjoy every minute of the time spent together. There is many more families and children that share the same disappointment.