Would it be too monotonous to rhyme a children’s book using the same technique for the whole book or is it essential that I change the style?
I'm having trouble recalling any rhyming book I read at that age (and I've got the Grinch and the Lorax partially commited to memory) that didn't violate the established pattern of rhymes... The opening page of the Lorax breaks the pattern, but it's a rare break (At the far end of town/ where the grickle grass grows/ and the wind smells still/ and sour when it blows/ and no birds ever sing/ excepting old crows/ is the street/ of the lifted Lorax), but the book follows an ABCBDB pattern for most of the story otherwise. The Grinch never deviates from an ABCB pattern (All the Whos down in Whoville/ Liked Christmas a lot/ But the Grinch, who lived just north of Whovill/ did not).
There is a strong case that Suess breaks formula only on the opening page, to add a critical establishing moment (Lorax: Emphasizing that this is the story of the origin of the Street's Name. Grinch: Establishes the Grinch is an outsider to the Whos and his rejection of Christmas).
The only other time I would recommend a subversive rhyme pattern would be if you're clearly set up to say a naughty word and do a last minute word swap... see the first Shrek Film and the little song about the rules of the Kingdom... notice which body part is facing the audience when they have to make a rhyme to the line "keep off the grass".
Overall though, the rhyme scheme should be kept the same because the pattern is going to carry the story and here the pattern is important for the children as the repetition is supposed to help with learning words and making memories. Consider the rhyming couplets used in "Green Eggs and Ham" where the story will do a long recursive list of conditions under which the character would not the titular feast. It's a long list, but can easily be remembered that he would not eat them in a box, he would not eat them with a fox, he would not eat them on a train, he would not eat them in the rain, he would not eat them hear or there, he would not eat them anywhere, for he does not like Green Eggs and Ham, he does not like them, Sam-I-Am.
And again, I remind you I am an adult and unaided gave a sample of several of Suess's lauded works (from memory, though I have no way of demonstrating that when writing) specifically because I'm looking to fill the rhyming pattern. And at the time I was a child, I had several adults convinced I could read at three years old, cause my finger would follow under the words I committed to memory (I was really imitating my parents, who both did the same thing as they read... but hey, gotta start somewhere).