Where should i put my kids' savings of 11k (11 y/o boy) and 15k (15 y/o girl)? I have NOT set aside their education fund. I may/may not need this fund for their education later on?

Just RSTU and forget about it.
$11k is $61,781 44 years later.
That's 10.49% p.a. How you gonna beat that for investment?
When the child grows up, he will manage his own investments him or herself. It is meaningless to invest for them, they won't appreciate or understand it. They have to do their own investments or not, depending on their characters and aptitude towards investments.
Pampering them may not be the best thing.

1. No. It's way too illiquid. Your children deserve some freedom in how they want to wield their savings.

2. No. For the same reasons as above.

3. Can but it will be under your name as they are too young to open an account. % depends on when you need the money. If they need it in 5 years, go for a lower % equities. If they need it in 20 years, feel free to go for 100% equities.

4. I prefer Endowus to MoneyOwl.

5. I've not used bank RSP but people have been mentioning FSMOne's RSP. Can check that out. As for endowment plans, better not, it's very illiquid for the first 20 years (or withdraw at a principal loss or loss taking into account inflation).