I have a grand daughter who is 2 1/2. He sees me building my Corsair and jumps right up on my lap and takes some scrap balsa and glue and builds her own 'airpwane" So, I know she has the interest.
I showed her my NexStar sim and she watched as I flew it. I gave her the radio, explained what the 'right' stick did "only that stick for now" and I took off and let he go for it. Believe it or not she did good until it was flying away towards her (how many of us had that problem in the beginning too). I would help her when needed, but she did pretty good for only being 2 1/2.

The one thing about the younguns - their attention span is short. She only flew for about a minute and a half and then she went to go color in her coloring book. But like rorrock said, don't push them into it.