“To” is the correct preposition. And yes, it is a preposition, so if it’s followed by a verb, we use the gerund form: “They took a liking to growing their own vegetables.” By the way, a decent dictionary should provide this information. https://idioms.thefreedictionary.com/take+a+liking+to https://www.merriam-webster.com/dictionary/take%20a%20liking%20to https://www.macmillandictionary.com/dictionary/british/take-a-liking-to https://en.wiktionary.org/wiki/take_a_liking_to

I think you are confusing two different expressions. We have the dynamic verb phrase 'take a liking to...' and the static verb phrase 'have a liking for...'.