I am a Ghanaian citizen with an Italian permanent residence but I have 3 kids who are Italian citizens with valid Italian passport. Do I need a visa to travel on holidays with my kids to the UK?
Yes, you need a visa. You need either a standard visitor visa or an EEA family permit for this purpose. To qualify for the latter, you must be dependent on one of your children who is traveling with you (for example, if you are retired, and your adult child is supporting you). Otherwise, you'll need the standard visitor visa.
(There is one exception. If you reside in Italy on the basis of your relationship with one of your children, and your residence card says explicitly that it is a permanent residence card of a citizen of the European Union, di familiare di un cittadino dell'unione, then you can travel with that child to the UK without a visa.)