Help

Have you tried using a reward chart? For every time they clean their room, they will get a star and after 10 stars, they will get a treat. Or something along those lines.

I think you should make a habbit of giving something they love most saying they will get that on cleaning the room and one more give them surprise gifts and kepp challenging them in between them and start praising them and their work, before the other for what they do in cleaning their room and i think this may work and i wish you all the best and yoir problem may clear in few days.

Make it really easy for them with lots of toy boxes and storage space. Make it fun, always help them and maybe put on some music and never make it seem like a chore. Do it everyday and then it can't get too wrecked and is faster for them and always reward them afterwards with something they like, maybe a drink and biscuit. The more enjoyable you can make this the more likely they are to do it.

Make a game out of it is one great way. One of my friends found an old small trophy at a garage sale, decorated it with sticker sna plastic jewels then have the kids race to clean their rooms. Whoever wins gets the trophy for the next day. They love it.

I tell them that if they don't clean their room and I end up doing it, I will start getting rid of stuff. They don't like that and usually start on it right away. Another thing I tried (my kids are also 6 & 4) was to make a game out of it. Put their favorite song on and tell them you want a certain area clean by the time the song is over (for my 6 year old son, an example would be his desk for my daughter it might be to get all her books back on her book shelf.) You don't have to reward them with something, just give them compliments like "I knew you could do it!" Or "I'm so proud of you". My kids really thrive on positive feed back. Yelling at them to get it done just frustrates everyone. If the room is REALLY bad, I will help to get them started or at least give them direction on where to start. Good luck!