Like every boy (and many girls), I went through that ubiquitous dinosaur phase, you know the one ;)
Also popular with kids is the 'mad scientist' phase... the one where if you were to, say, combine a rhino and an iguana, you might get this:
It was at this point I realised that I'd basically drawn the (very) dated, Crystal Palace
Iguanodon (1852), which sports the cool nose-spike;
"...their thumb spikes were mistaken for horns, and they were depicted as elephant-like quadrupeds...".
Crazy!