Nearly half of parents admit being "piggy bank raiders" who dip into their children's cash to pay for parking, takeaways, taxis, school trips and the window cleaner.
Some 46% of parents of children aged between four and 16 said they have taken cash from their child's piggy bank stash, a survey from Nationwide Savings has found.
The average amount taken over the past 12 months was £21.41, while one in 10 (10%) parents had taken £50 or more.
Mums are more likely to raid their child's piggy bank than dads - but dads are more likely to swipe bigger amounts, the survey found.
The months after Christmas, when many families are getting their finances back on track, also appears to be the time when piggy bank raiders are most prolific, with many parents saying they tended to take money between January and April.
The survey of 2,000 parents found those in Yorkshire and the Humber, the North East and the South West are the most likely to raid their child's piggy bank.
Here are the main reasons for piggy bank raiding parents taking the cash, according to the research for Nationwide Savings:
1. To pay school lunch money, 15%
2. To pay a bill, 15%
3. School trips, 11%
4. Parking, 11%
5. Other (included paying bus fares, a milkman, taxis, a cleaner, hair cuts, a window cleaner, petrol and the tooth fairy), 12%
6. I was broke, 8%
7. Takeaways, 5%
The vast majority of parents (93%) said they put the money back afterwards - and only around two in five (39%) of children noticed the money had disappeared.
Nearly one third of parents who took money said they had confessed to their child, while 23% sneaked the money back into their child's piggy bank. A further one in seven (14%) added "interest" onto the amount they had borrowed, putting more money in than they had taken out.
Andrew Baddeley-Chappell, Nationwide's head of savings and mortgage policy, said: "Despite being in charge of instilling a good approach to finance, almost half of parents have been caught in spring raids on their kid's piggy bank stash.
"While liberating change for parking or to pay school lunch money could be viewed as excusable, one in 10 parents actually borrowed more than £50 in the last year, including for paying bills.
"Although more than half of kids don't even notice the money has gone, it is reassuring that the vast majority of parents - including me - pay the cash back, with one in seven paying back even more than they borrowed to ease their guilt.
"Based on these findings, perhaps there are even more reasons for parents to encourage their kids to start the savings habit."