He lies because he is embarrassed. It’s embarrassing issue for him. No matter how you slice it. What you can do is make a chart and for every day he stays dry he will receive a sticker and if he fills a week with stickers then he gets a prize. If he wets himself just let him know he can turn it around and do better tomorrow or at night if he wakes up dry. Maybe giving him an incentive (prize) might make him stay dry. Also keep him on a schedule to go to the bathroom. Make him go every hour after drinking. Stop all liquids an hour or a half hour before bed time. Wake him up at night to go pee. It will be hard on you because youlll loose sleep doing this but if u stay consistent you’ll get success.
You are successful!

Potty Training Problems.....For the Parent of the the child who is WETTING His Pants.You brought up a VERY Important point.You said that your son DOESNT Wet himself AT SCHOOL or ANY Where Else.... Only AT HOME.That tells me and should be a CLUE for you as well that your son DOES have Control over his Bladder and What he is doing.He may just be TOO BUSY to be BOTHERED going to the Toilet or else he is WAITING Too Long until its Too Late to HOLD It in.Something else you may Not realize but at School there are ALWAYS SCHEDULED Bathroom Breaks and SPECIFIC times when EVERYONE is Expected to STOP What they are Doing to go. You mentioned your sons 4 year old Sibling......I would suggest you have Designated BATHROOM BREAKS ....Every day......for ALL of your Children .....Wether they SAY they NEED to go or not,No Matter What, to help Enforce the New Rule and Reinforce the Idea to help make it a HABIT at Home.I cant remember you mentioning How OLD your son is,...... only that you said he has a younger 4 year old Sibling.....But If he is older than 4 then he is Definately OLD enough to KNOW that WHAT he is Doing is WRONG.He is PEEing in His Pants then Denying and Lying about it....That should tell you that Your Son KNOWS that it is WRONG and is Well Aware that it is Considered UNACCEPTABLE with YOU ....Otherwise he would Not be Denying it , Lying about it or Trying to Hide it from you.He also knows it is Not considered Acceptable Behavior at SCHOOL or in other PUBLIC PLACES or he would be definately be having Toileting Accidents elsewhere. I suggest if Nothing Else .....give your Son the Responsibility of all of his PEE PEED Laundry and have him Hand Wash ALL of his WET Pants, Shorts, Pajama Bottoms and Underwear as it Occurs....either in the Bathroom sink or in a Plastic Dish or Wash Tub and then you can either hang them over the BathTub or the Shower Rod or else put them in the Dryer to dry. have a child that is Extremely High Functioning in most other areas anyway but seems to think Nothing about walking around All day in his Wet Peed Pants and Underwear......... at Home AND in Public Places.For him we are looking into the possibility that it might be a Neurological cause or else Lack of Maturity and Self Awareness or maybe even lack of Care and Concern about his own Personal Hygene.Whatever the reason we expect him to be Responsible for attending to his own Personal Care and Hygiene since he is MORE than Capable of Physically doing so.So even if your Son doesnt Care and or if he seems to be Oblivious to being in Wet Pants and Underwear .....Peeing in his Pants and Smelling like URINE is NOT Acceptable ANYWHERE in ANY Social Situation and most certainly wont be Tolerated by Anyone( Not by his friends and classmates and not by other Adults either) so it is Most Definately a Bad Habit / or Obvious Problem and should NOT be Ignored.

About the 7 year old that keeps Peeing himself. (Email address can only be seen by the question and answer creators), YOU ARE RIGHT, BOYS CAN BE TRICKY!!!!....Thats partly because they ARE VERY DIFFERENT from Girls and Mature at a Different rate than Girls do. Even if a Boy and a Girl Both happen to be on the Spectrum and are Twins ....They are often STILL Very Different from one another........

Pee pee alarms are what we always use. If he has a tablet or computer time you can set it up on there so he stops to pee. A good old fashion oven or microwave timer works great too. Also ask his teacher what their bathroom schedule is and follow that...seems to be working. He may just be lying because he's embarrassed about it...my daughter will lie when she's ashamed. You can start a reward system too for whenever he goes or even changes himself if he's wet to encourage it. I've known nt boys especially who have wet themselves until 10+ years old...boys can be tricky.