Having attained new developmental goals like standing and walking, your child’s once-predictable sleeping pattern has become less dependable. Morning and afternoon naps have become less regular, and he's probably waking up more frequently at night. He may spend his cot time moving up and down instead of sleeping, and that's okay. Eventually, once the novelty of walking wears off, your child will return to a more settled state. Until then, keep putting him in his cot at nap time, but don't worry if he doesn't sleep.
At night, sleep disruption is even more likely. You can help your child get back to sleep by reacting calmly and firmly, and reinstating all the familiar rituals. Give him about 10 minutes to go to sleep on his own. Go in and pat him softly to reassure him you're there, and then leave.
Eating patterns may also be disrupted. Your child may eat next to nothing at one meal and more than you do at the next. He'll balance it out just fine as long as you don't make a big deal out of it. In between meals, offer high-energy snacks such as a bagel with cream cheese.