We used to always go to the farm show in Harrisburg. It's really cute, but it gets way over-crowded, parking is terrible, and it's almost impossible to go to if you have a child in a stroller. I'd reccomend it if you only have 1 or 2 children or have plenty of adult help. We have 6 children now, so we just stick with visiting the local farms!
The big downside of the farm show is the crowds, but if you are not pushing a stroller it helps. Try to find a time to go when you think it might be a little more empty, and make sure to give yourselves plenty of time because there is a a lot to see. My kids ask to go every year because they love all the animals, cowboy stuff, tractors, etc. Plus, it's a good indoor thing to do in winter. The food is pretty expensive, but you also can get lots of free samples walking through the vendors selling food. Watch out for the salsa labeled "hot". If you have time the rodeo is a fun thing to take in also, it is only on certain nights and does cost extra.
The Farm Show in Harrisburg is the largest indoor agricultural exhibit on the eastern seaboard. I grew up going every year with my family! Where else can you see a lifesize butter scultpure, eat potato doughnuts, fried mushrooms, and fresh milkshakes, and even weigh your entire family on an industrial scale! The Farm Show is huge and more than worth the time!
I highly recommend wearing shoes you don't mind tossing out afterwards. You WILL step in poop!
In the first weeks of the new year, there isnt alot people can get out to do in York County. However... the Farm Show Complex is always a hot spot at this time of year. Between the livestock competition, the rodeos, presentations, and kids activities... it'll keep you busy! Do be prepared to pay for parking, and food! Some events may cost extra as well. most of the kids activities are free though.
***As of 2011, parking was $10, Funnel cake is $5, and the Merry go Round is $2... I think the Rodeo was $15 for adults, but I'm not positive on that pricing.