Hi Sheila,
Apologies, just to clarify, it is completely acceptable to do the bookkeeping for your son, however, he is legally responsible for the accuracy of the data inputted.
The important thing is that your son will need to submit the Quarterly updates. In this case, if you choose to do the bookkeeping on his behalf, you can hover over your business name at the top right > Then click Add Business. Once added, you will need to upgrade to the Sole Trader paid plan where you will then have the ability to invite him in via the Building Icon (top right) > Manage users > Invite user. He will then be able to log in with his own credentials and submit the Quarterly updates.
For his property business, you can also add this via the same navigation steps above and invite him in.
Tommy