The only time Lalli had kinda-sorta fluffy hair (coming out of the Mora baths) Emil was compelled to tidy it for him. I tend to struggle with his hair shape, too. The fringe is tucked (presumably behind his ears?) under an oddly square shape, so severely straight in the front that you never see his ears. He has a bob haircut, slightly shorter in the back.
He has a ski-slope nose, as do all the Hotakainens. This is a real shape (I have one too), and different from a pug nose where the front is flattened back. The bridge is fairly flat, and it turns upward at the end.
His eyes are gorgeous. Minna tends to stylise the irises and pupils of all her characters (Kitty is the only one with round ones!); Lalli has ended up with cat-like slits more often than not.