Some warning signs that your child may be developmentally delayed include not walking, if your child is not talking, if they're not engaged with you. Engaged is this feeling that you get when your child is able to look at you. When you say their name and they turn, they're responsive. If they're not able to be responsive, if they're not coming towards you when you're calling them, if they're being withdrawn, if they don't want to interact with their peers, these are all signs that your child may be delayed.
Other signs include things such as if they're clumsy, if they're walking into things all the time, if they don't want to engage in sports or in the playground, if they don't want to play with their peers, if they have a hard time holding a pencil or a crayon. These are all sign that your child can be delayed.
The important thing to know is to observe their behavior. Always, if you can, document it, because maybe it's a one off. Maybe one day they didn't feel like holding a pencil, but in general they can. But if they continuously cannot do these simple things and you're observing them, or if they're having times when they're getting extremely upset or angry, write down what you see and speak with your child's pediatrician and share with them the concerns that you're having. Be as detailed as you can so your pediatrician can work with you on what the best steps to take are.