Keep in mind that you will need also an video editing application if this "voiceover" will be added post-factum. As for microphone - you can start practicing with any $20 (or GPB 15, as you seem to be Briton) headset.
youtube account holders must be 18+ unless a parent signs up for a child in which case they must be 13+. by the rules your son must be at least 4 years older before he starts doing his own videos. please keep that in mind.
cheap microphones? snowball ice or something from neewer
Keep in mind that you will need also an video editing application if this "voiceover" will be added post-factum. As for microphone - you can start practicing with any $20 (or GPB 15, as you seem to be Briton) headset.
The Blue Snowball is a fantastic microphone for the money. It captures studio quality sound for around $60. There is also a cheaper version, but it's more condensed, so the quality won't be as good.