Took my Son out from 2 years old...now he is 19, and loves Ice fishing...Daughter started at two also...now at 11, she goes out a few times each year, on nicer days, and witht he shanty...
Lots of good suggestions....A Game Boy, would have helped( never had one) But I did always take a few small toys out for them to play with, and kept the trips very short...prolly 2-3 hours MAX the first few years, then went to a petting farm, hike in the woods, or anything else to make it a day long event for them.
Samantha will stay out longer now, and she is looking forward to going this year..I hope to get her onto some better fishing...maybe a nice pike on a tip-up..she would love it..
SOmeone else said it right....do your very best to put them on fish, even DINKS....if they don't catch something...they don't want to go back...