I know someone who, when he was about 5 years old, I want to be a fireman in the morning and a tzadik in the afternoon.
He is now mid-30s and a (very competent) electrical engineer, who runs a morning chaburah in our shul.
But to the original question, the answer is; don’t take it too seriously when they are very little. Just today my son told me, he wants to be an astronaut, soldier, fisherman, pirate, deep sea diver and firefighter. Tomorrow it’ll be another load of things. If he’s still saying all that at 16, I would have to take advice.