My 20 month old doesn’t say many words


My little is 20 months old hardly says any words. He only says here,what, this and his sister name that’s it. He understands when I say it’s nap time or bed time and will go to the stair gates. He will give us a kiss when we ask him and he will give me his teddy to kiss and cuddle. He also helps me tidy up his toys when he wants to but he doesn’t say many words. He also bubbles a lot. I am really worried there is sometimes wrong with him. My sister and mum tell me not to worry and he will develop in his own time but my niece is only 5 months older and she can talk in sentences. My two older children spoke by his age I am so worried 😢