diff --git a/src/node/mod.rs b/src/node/mod.rs
index 987440a..0e67b0f 100644
--- a/src/node/mod.rs
+++ b/src/node/mod.rs
@@ -8,13 +8,19 @@ mod node_modifier;
 pub struct Node {
     children: Vec<Node>,
     handler: NodeHandler,
+    max_children_count: Option<usize>,
 }
 
 impl Node {
-    pub fn new(children: Option<Vec<Node>>, handler: NodeHandler) -> Self {
+    pub fn new(
+        children: Option<Vec<Node>>,
+        handler: NodeHandler,
+        max_children_count: Option<usize>,
+    ) -> Self {
         Self {
             children: children.unwrap_or(vec![]),
             handler: handler,
+            max_children_count,
         }
     }
     pub fn get_value(&self) -> f64 {
@@ -35,18 +41,21 @@ impl Node {
         Node {
             children: vec![],
             handler: NodeHandler::Number { number: n },
+            max_children_count: None,
         }
     }
     pub fn function(func: fn(Vec<f64>) -> f64) -> Node {
         Node {
             children: vec![],
             handler: NodeHandler::Function { function: func },
+            max_children_count: Some(1),
         }
     }
     pub fn variable(getter: fn() -> f64) -> Node {
         Node {
             children: vec![],
             handler: NodeHandler::Variable { getter },
+            max_children_count: Some(0),
         }
     }
 }
diff --git a/src/node/node_modifier.rs b/src/node/node_modifier.rs
index 5f8fd33..ac2f932 100644
--- a/src/node/node_modifier.rs
+++ b/src/node/node_modifier.rs
@@ -1,10 +1,14 @@
 use crate::node::Node;
+use crate::node::NodeHandler;
 use crate::node::functions;
-use crate::node::handler::NodeHandler;
 use rand::random_range;
 
 const PICK_STOP_PROBABILITY: u8 = 2;
 
+pub enum NodeManipulationError {
+    TooMuchChildren(Node),
+}
+
 pub struct NodeModifier<'a> {
     picked_node: &'a mut Node,
     function_mutation_pool: Vec<fn(Vec<f64>) -> f64>,
@@ -57,16 +61,33 @@ impl<'a> NodeModifier<'a> {
         }
     }
 
-    pub fn add_node(&mut self, node: Node) {
+    pub fn add_node(&mut self, node: Node) -> Result<(), NodeManipulationError> {
+        if let Some(x) = self.picked_node.max_children_count {
+            if self.picked_node.children.len() + 1 >= x {
+                return Err(NodeManipulationError::TooMuchChildren(node));
+            }
+        }
         self.picked_node.children.push(node);
+        Ok(())
     }
 
-    pub fn insert_node(&mut self, mut node: Node, between: Option<usize>) {
+    pub fn insert_node(
+        &mut self,
+        mut node: Node,
+        between: Option<usize>,
+    ) -> Result<(), NodeManipulationError> {
+        if let Some(x) = self.picked_node.max_children_count {
+            if self.picked_node.children.len() + 1 >= x {
+                return Err(NodeManipulationError::TooMuchChildren(node));
+            }
+        }
         let children_count = self.picked_node.children.len();
         let operated_index = between.unwrap_or(random_range(0..children_count));
         let moved = self.picked_node.children.remove(operated_index);
         node.children.push(moved);
         self.picked_node.children.insert(operated_index, node);
+
+        Ok(())
     }
 
     pub fn mutate_node(&mut self) {