Take up the complaint with the tour operator if that is how you booked. If you booked through a travel agent then you need to write to them enclosing any paperwork and preferably include photos.
You may also be asked to provide all of the photos from your holiday (usually those where all the family can be seen having a great time as well).
You need to register your complain in writing within 28 days of your returning back to UK at the end of your holiday.
Wait for the acknowledgement and at least a first reply.
If you don't get a satisfactory response which may or may not include compensation and if you feel the operator has breached a contract or failed in their duty of care - you can decide if you should take the matter further, to Abta for instance. If this is what you wish to do, you must write back and await a further reply before Abta will even entertain your paperwork and issues. Each party must pay a fee to take a claim to Abta.
If you've been offered compensation and you take it to Abta and lose your claim, you are responsible for all fees and you also lose the original offer of compensation.
The alternative to that is to take the matter up with your local County Court as a civil matter/personal injury claim (if indeed this is what it amounts to) and it used to be for claims up to 5000 GBP when I lived in UK and worked in the County Court (before working at FCH).
To do this will incur fees which you must pay to issue the summons and at each stage along the way - these do get added to the person you are claiming against (if you win the case).
A number of operators/agents will settle at the very last minute on the court steps - others don't and therefore you have to hope the registrar will decide in your favour.

Lots of things to consider as well as what the basis of your complaint is before taking any action....but your original post mentions compensation so of course, we will assume that is what you were looking for based on your question.