'Assault by beating' is simply an alternative wording for 'common assault, which is the lowest level of assault charge. (Simply pushing someone very lightly or even ruffling their hair against their wishes in enough to constitute 'common assault').
From the limited information you've provided it seems very unlikely that the court would take the view that it's a 'Category 1' offence (where both 'harm' and 'culpability' are rated as 'high). If it's rated as 'Category 3' (with both of those factors 'low') you'll almost certainly just be fined (plus costs plus a £25 'victim surcharge'). If it's 'Category 2' you could still just face a fine but you might be given a Community Order (i.e. unpaid work) instead.
See pages 213 to 215 here:
http://www.sentencingcouncil.org.uk/wp-content/uploads/MCSG_web_-_October_2014.pdf